diff --git a/Package.swift b/Package.swift
index 4c9c5cae3..bdc6b8dd8 100644
--- a/Package.swift
+++ b/Package.swift
@@ -543,7 +543,8 @@ var targets: [Target] = [
   .testTarget(
     name: "SwiftSyntaxCodeActionsTests",
     dependencies: [
-      "SwiftSyntaxCodeActions"
+      "SwiftSyntaxCodeActions",
+      "SKTestSupport",
     ]
       + swiftSyntaxDependencies([
         "SwiftParser",
diff --git a/Sources/SwiftSyntaxCodeActions/MoveMembersToExtension.swift b/Sources/SwiftSyntaxCodeActions/MoveMembersToExtension.swift
new file mode 100644
index 000000000..592b9facc
--- /dev/null
+++ b/Sources/SwiftSyntaxCodeActions/MoveMembersToExtension.swift
@@ -0,0 +1,467 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2026 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+@_spi(SourceKitLSP) import LanguageServerProtocol
+import SwiftBasicFormat
+import SwiftRefactor
+package import SwiftSyntax
+
+package struct MoveMembersToExtension: SyntaxRefactoringProvider {
+  package struct Context {
+    let range: Range<AbsolutePosition>
+
+    package init(range: Range<AbsolutePosition>) {
+      self.range = range
+    }
+  }
+
+  package static func refactor(syntax: SourceFileSyntax, in context: Context) throws -> SourceFileSyntax {
+    let sourceDecl = try findSourceDecl(syntax: syntax, range: context.range)
+    let selectedMembers = findSelectedMembers(declGroup: sourceDecl.declGroup, range: context.range)
+    let membersToMove = try validateMovableMembers(selectedMembers: selectedMembers)
+    let remainingMembers = updateRemainingMembers(declGroup: sourceDecl.declGroup, membersToMove: membersToMove)
+
+    var updatedDeclGroup = sourceDecl.declGroup
+    updatedDeclGroup.memberBlock = updateMemberBlock(
+      sourceDecl.declGroup.memberBlock,
+      members: remainingMembers
+    )
+
+    let extensionDecl = makeExtension(sourceDecl: sourceDecl, membersToMove: membersToMove)
+
+    return updateSyntax(
+      syntax,
+      sourceDecl: sourceDecl,
+      updatedDeclGroup: updatedDeclGroup,
+      extensionDecl: extensionDecl
+    )
+  }
+}
+
+private enum ValidationResult: CustomStringConvertible {
+  case accessor
+  case deinitializer
+  case enumCase
+  case storedProperty
+
+  var description: String {
+    switch self {
+    case .accessor: return "accessor"
+    case .deinitializer: return "deinitializer"
+    case .enumCase: return "enum case"
+    case .storedProperty: return "stored property"
+    }
+  }
+
+  /// Validates that `member` can be moved to an extension. If it can, return `nil`, otherwise return the reason why
+  /// `member` cannot be moved to an extension.
+  init?(_ member: MemberBlockItemSyntax) {
+    switch member.decl.kind {
+    case .accessorDecl:
+      self = .accessor
+    case .deinitializerDecl:
+      self = .deinitializer
+    case .enumCaseDecl:
+      self = .enumCase
+    default:
+      if let varDecl = member.decl.as(VariableDeclSyntax.self),
+        varDecl.bindings.contains(where: { $0.accessorBlock == nil || $0.initializer != nil })
+      {
+        self = .storedProperty
+      } else {
+        return nil
+      }
+    }
+  }
+}
+
+private extension MoveMembersToExtension {
+  struct MemberToMove {
+    struct NestedMember: Equatable {
+      let updatedMember: MemberBlockItemSyntax
+      let partsToMove: [MemberBlockItemSyntax]
+      let validationResults: [ValidationResult]
+      let path: [String]
+      let indentationToRemove: Trivia
+    }
+
+    enum Scope: Equatable {
+      case inner
+      case nested(NestedMember)
+    }
+
+    let member: MemberBlockItemSyntax
+    let scope: Scope
+
+    var validationResults: [ValidationResult] {
+      switch scope {
+      case .inner:
+        return [ValidationResult(member)].compactMap { $0 }
+
+      case .nested(let nested):
+        return nested.validationResults
+      }
+    }
+
+    var hasMovableMembers: Bool {
+      switch scope {
+      case .inner:
+        return ValidationResult(member) == nil
+
+      case .nested(let nested):
+        return !nested.partsToMove.isEmpty
+      }
+    }
+
+    init(
+      member: MemberBlockItemSyntax,
+      scope: Scope = .inner
+    ) {
+      self.member = member
+      self.scope = scope
+    }
+  }
+
+  struct SourceDecl {
+    let statement: CodeBlockItemSyntax
+    let index: CodeBlockItemListSyntax.Index
+    let declGroup: any DeclGroupSyntax
+    let declName: TokenSyntax
+  }
+
+  static func findSourceDecl(syntax: SourceFileSyntax, range: Range<AbsolutePosition>) throws -> SourceDecl {
+    guard
+      let statement = syntax.statements.first(where: { $0.item.range.contains(range) }),
+      let decl = statement.item.asProtocol((any NamedDeclSyntax).self),
+      let declGroup = statement.item.asProtocol((any DeclGroupSyntax).self),
+      let index = syntax.statements.index(of: statement)
+    else {
+      throw RefactoringNotApplicableError("Type declaration not found")
+    }
+
+    return SourceDecl(statement: statement, index: index, declGroup: declGroup, declName: decl.name)
+  }
+
+  static func findSelectedMembers(declGroup: any DeclGroupSyntax, range: Range<AbsolutePosition>) -> [MemberToMove] {
+    declGroup.memberBlock.members.compactMap { member in
+      guard range.overlaps(member.trimmedRange) else { return nil }
+
+      if let nestedMember = findNestedMovableMember(member: member, range: range) {
+        return MemberToMove(
+          member: member,
+          scope: .nested(nestedMember)
+        )
+      }
+
+      return MemberToMove(member: member)
+    }
+  }
+
+  static func validateMovableMembers(selectedMembers: [MemberToMove]) throws -> [MemberToMove] {
+    let membersToMove = selectedMembers.filter(\.hasMovableMembers)
+
+    guard !membersToMove.isEmpty else {
+      let notMovedMembers = Set(selectedMembers.flatMap(\.validationResults))
+        .map(\.description)
+        .sorted().joined(separator: ", ")
+      throw RefactoringNotApplicableError(
+        "Cannot move \(notMovedMembers) to extension"
+      )
+    }
+
+    return membersToMove
+  }
+
+  static func updateRemainingMembers(
+    declGroup: any DeclGroupSyntax,
+    membersToMove: [MemberToMove]
+  ) -> [MemberBlockItemSyntax] {
+
+    let wholeMembers = membersToMove.compactMap { move in
+      if case .inner = move.scope {
+        return move.member
+      }
+      return nil
+    }
+
+    var remainingMembers = Array(declGroup.memberBlock.members).filter { !wholeMembers.contains($0) }
+
+    for index in remainingMembers.indices {
+      guard let move = membersToMove.first(where: { $0.member == remainingMembers[index] }),
+        case .nested(let nested) = move.scope
+      else {
+        continue
+      }
+
+      remainingMembers[index] = nested.updatedMember
+    }
+
+    return remainingMembers
+  }
+
+  static func updateMemberBlock(
+    _ memberBlock: MemberBlockSyntax,
+    members: [MemberBlockItemSyntax]
+  ) -> MemberBlockSyntax {
+    var memberBlock = memberBlock
+    var members = members
+
+    if members.isEmpty {
+      memberBlock.members = MemberBlockItemListSyntax()
+      memberBlock.rightBrace.leadingTrivia = Trivia()
+      return memberBlock
+    }
+
+    members[0].leadingTrivia = .newline.merging(
+      members[0]
+        .leadingTrivia
+        .trimmingPrefix(while: \.isNewline)
+    )
+
+    let lastIndex = members.index(before: members.endIndex)
+
+    members[lastIndex].trailingTrivia =
+      members[lastIndex]
+      .trailingTrivia
+      .trimmingSuffix(while: \.isNewline)
+
+    memberBlock.members = MemberBlockItemListSyntax(members)
+    return memberBlock
+  }
+
+  static func findNestedMovableMember(
+    member: MemberBlockItemSyntax,
+    range: Range<AbsolutePosition>
+  ) -> MemberToMove.NestedMember? {
+    guard let memberGroup = member.decl.asProtocol((any DeclGroupSyntax).self),
+      let memberName = member.decl.asProtocol((any NamedDeclSyntax).self)?.name.text
+    else {
+      return nil
+    }
+
+    var currentGroup = memberGroup
+    var path = [memberName]
+    var declGroups = [(declGroup: any DeclGroupSyntax, index: Int)]()
+
+    while true {
+      let members = Array(currentGroup.memberBlock.members)
+
+      let selectedIndices = members.indices.filter { range.overlaps(members[$0].trimmedRange) }
+
+      guard selectedIndices.count == 1,
+        let selectedIndex = selectedIndices.first,
+        let childGroup = members[selectedIndex].decl.asProtocol((any DeclGroupSyntax).self),
+        let childName = members[selectedIndex].decl.asProtocol((any NamedDeclSyntax).self)?.name.text,
+        childGroup.memberBlock.members.contains(where: { range.overlaps($0.trimmedRange) })
+      else {
+        break
+      }
+
+      declGroups.append((currentGroup, selectedIndex))
+
+      currentGroup = childGroup
+      path.append(childName)
+    }
+
+    let selectedMembers = Array(currentGroup.memberBlock.members).filter { range.overlaps($0.trimmedRange) }
+
+    guard !selectedMembers.isEmpty else { return nil }
+
+    let partsToMove = selectedMembers.filter { ValidationResult($0) == nil }
+
+    let validationResults = selectedMembers.compactMap(ValidationResult.init)
+
+    let remainingMembers = selectedMembers.filter { !partsToMove.contains($0) }
+
+    var updatedGroup = currentGroup
+    updatedGroup.memberBlock = updateMemberBlock(currentGroup.memberBlock, members: remainingMembers)
+
+    for (declGroup, index) in declGroups.reversed() {
+      var parentMembers = Array(declGroup.memberBlock.members)
+
+      parentMembers[index].decl = DeclSyntax(updatedGroup)
+
+      var updatedParent = declGroup
+      updatedParent.memberBlock.members = MemberBlockItemListSyntax(parentMembers)
+      updatedGroup = updatedParent
+    }
+
+    var updatedMember = member
+    updatedMember.decl = DeclSyntax(updatedGroup)
+
+    let indentationToRemove =
+      currentGroup
+      .firstToken(viewMode: .sourceAccurate)?
+      .indentationOfLine
+      ?? Trivia()
+
+    return MemberToMove.NestedMember(
+      updatedMember: updatedMember,
+      partsToMove: partsToMove,
+      validationResults: validationResults,
+      path: path,
+      indentationToRemove: indentationToRemove
+    )
+  }
+
+  static func unindentExtensionMembers(
+    _ members: [MemberBlockItemSyntax],
+    by indentation: Trivia
+  ) -> [MemberBlockItemSyntax] {
+    members.map { member in
+      let remover = IndentationRemover(
+        indentation: indentation,
+        indentFirstLine: true
+      )
+
+      return
+        remover
+        .rewrite(member)
+        .as(MemberBlockItemSyntax.self)
+        ?? member
+    }
+  }
+
+  static func makeExtensionName(
+    rootName: TokenSyntax,
+    path: [String]
+  ) -> TypeSyntax {
+    var rootName = rootName
+    rootName.leadingTrivia = Trivia()
+    rootName.trailingTrivia = Trivia()
+
+    var type = TypeSyntax(
+      IdentifierTypeSyntax(
+        leadingTrivia: .space,
+        name: rootName
+      )
+    )
+
+    for component in path {
+      type = TypeSyntax(
+        MemberTypeSyntax(
+          baseType: type,
+          period: .periodToken(),
+          name: .identifier(component)
+        )
+      )
+    }
+
+    type.trailingTrivia = .space
+    return type
+  }
+
+  static func makeExtension(sourceDecl: SourceDecl, membersToMove: [MemberToMove]) -> ExtensionDeclSyntax {
+    var extensionMembers = [MemberBlockItemSyntax]()
+    var declName = sourceDecl.declName
+    declName.trailingTrivia = declName.trailingTrivia.merging(.space)
+
+    let extendedType: TypeSyntax
+
+    if membersToMove.count == 1,
+      case .nested(let nested) = membersToMove[0].scope
+    {
+      extensionMembers = unindentExtensionMembers(
+        nested.partsToMove,
+        by: nested.indentationToRemove
+      )
+
+      extendedType = makeExtensionName(
+        rootName: sourceDecl.declName,
+        path: nested.path
+      )
+    } else {
+      extensionMembers = membersToMove.map(\.member)
+
+      extendedType = makeExtensionName(
+        rootName: sourceDecl.declName,
+        path: []
+      )
+    }
+
+    extensionMembers[0].leadingTrivia = .newline.merging(
+      extensionMembers[0].leadingTrivia.trimmingPrefix(while: \.isNewline)
+    )
+
+    var memberBlock = sourceDecl.declGroup.memberBlock
+    memberBlock.members = MemberBlockItemListSyntax(extensionMembers)
+
+    return ExtensionDeclSyntax(
+      leadingTrivia: .newlines(2),
+      extendedType: extendedType,
+      memberBlock: memberBlock
+    )
+  }
+
+  static func updateSyntax(
+    _ syntax: SourceFileSyntax,
+    sourceDecl: SourceDecl,
+    updatedDeclGroup: any DeclGroupSyntax,
+    extensionDecl: ExtensionDeclSyntax
+  ) -> SourceFileSyntax {
+    var syntax = syntax
+    syntax.statements[sourceDecl.index] = sourceDecl.statement.with(\.item, .decl(DeclSyntax(updatedDeclGroup)))
+    syntax.statements.insert(
+      CodeBlockItemSyntax(item: .decl(DeclSyntax(extensionDecl))),
+      at: syntax.statements.index(after: sourceDecl.index)
+    )
+    return syntax
+  }
+}
+
+extension MoveMembersToExtension: ResolvableSyntaxRefactoringCodeActionProvider {
+  static func refactoringContext(
+    for node: SwiftSyntax.SourceFileSyntax,
+    in scope: SyntaxCodeActionScope
+  ) -> RefactoringContext<Context, EmptyLSPCodable> {
+    .context(Context(range: scope.range))
+  }
+
+  static func resolveContext(
+    for data: UnresolvedData,
+    in scope: SyntaxCodeActionScope,
+    symbolInfo: (_ position: Position) async throws -> [SymbolDetails]
+  ) async throws -> Context {
+    Context(range: scope.range)
+  }
+
+  typealias UnresolvedData = EmptyLSPCodable
+
+  static var title: String { "Move to extension" }
+
+  static func nodeToRefactor(in scope: SyntaxCodeActionScope) -> SourceFileSyntax? {
+    guard scope.range.lowerBound != scope.range.upperBound else {
+      return nil
+    }
+
+    return scope.file
+  }
+}
+
+fileprivate extension Trivia {
+  func trimmingPrefix(
+    while predicate: (TriviaPiece) -> Bool
+  ) -> Trivia {
+    Trivia(pieces: self.drop(while: predicate))
+  }
+
+  func trimmingSuffix(
+    while predicate: (TriviaPiece) -> Bool
+  ) -> Trivia {
+    Trivia(
+      pieces: self[...]
+        .reversed()
+        .drop(while: predicate)
+        .reversed()
+    )
+  }
+}
diff --git a/Sources/SwiftSyntaxCodeActions/SyntaxCodeActions.swift b/Sources/SwiftSyntaxCodeActions/SyntaxCodeActions.swift
index 61eae4191..aa2636d9f 100644
--- a/Sources/SwiftSyntaxCodeActions/SyntaxCodeActions.swift
+++ b/Sources/SwiftSyntaxCodeActions/SyntaxCodeActions.swift
@@ -34,6 +34,7 @@ package let allSyntaxCodeActionProviders: [any SyntaxCodeActionProvider.Type] =
     GenerateEnumCaseAsAccessors.self,
     GenerateEnumCaseIsAccessors.self,
     MigrateToNewIfLetSyntax.self,
+    MoveMembersToExtension.self,
     OpaqueParameterToGeneric.self,
     RemoveRedundantParentheses.self,
     RemoveSeparatorsFromIntegerLiteral.self,
@@ -47,5 +48,6 @@ package let allSyntaxCodeActionProviders: [any SyntaxCodeActionProvider.Type] =
 
 package let supersededSourcekitdRefactoringActions: Set<String> = [
   "source.refactoring.kind.convert.to.computed.property",  // Superseded by ConvertStoredPropertyToComputed
+  "source.refactoring.kind.move.members.to.extension",  // Superseded by MoveMembersToExtension
   "source.refactoring.kind.simplify.long.number.literal",  // Superseded by AddSeparatorsToIntegerLiteral
 ]
diff --git a/Tests/SwiftSyntaxCodeActionsTests/MoveMembersToExtensionTests.swift b/Tests/SwiftSyntaxCodeActionsTests/MoveMembersToExtensionTests.swift
new file mode 100644
index 000000000..26195f506
--- /dev/null
+++ b/Tests/SwiftSyntaxCodeActionsTests/MoveMembersToExtensionTests.swift
@@ -0,0 +1,330 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2026 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+import SKTestSupport
+import SwiftParser
+import SwiftRefactor
+import SwiftSyntax
+import SwiftSyntaxBuilder
+import SwiftSyntaxCodeActions
+import XCTest
+
+final class MoveMembersToExtensionTests: XCTestCase {
+  func testMoveFunctionFromClass() throws {
+    try assertMoveMembersToExtension(
+      """
+      class Foo {1️⃣
+        func foo() {
+          print("Hello world!")
+        }2️⃣
+
+        func bar() {
+          print("Hello world!")
+        }
+      }
+      """,
+      expected:
+        """
+        class Foo {
+          func bar() {
+            print("Hello world!")
+          }
+        }
+
+        extension Foo {
+          func foo() {
+            print("Hello world!")
+          }
+        }
+        """
+    )
+  }
+
+  func testMoveParticiallySelectedFunctionFromClass() throws {
+    try assertMoveMembersToExtension(
+      """
+      class Foo {
+        func foo() {
+          1️⃣print("Hello world!")
+        }2️⃣
+
+        func bar() {
+          print("Hello world!")
+        }
+      }
+
+      struct Bar {
+        func foo() {}
+      }
+      """,
+      expected:
+        """
+        class Foo {
+          func bar() {
+            print("Hello world!")
+          }
+        }
+
+        extension Foo {
+          func foo() {
+            print("Hello world!")
+          }
+        }
+
+        struct Bar {
+          func foo() {}
+        }
+        """
+    )
+  }
+
+  func testMoveSelectedFromClass() throws {
+    try assertMoveMembersToExtension(
+      """
+      class Foo {1️⃣
+        func foo() {
+          print("Hello world!")
+        }
+
+        deinit() {}
+
+        func bar() {
+          print("Hello world!")
+        }2️⃣
+      }
+
+      struct Bar {
+        func foo() {}
+      }
+      """,
+      expected:
+        """
+        class Foo {
+          deinit() {}
+        }
+
+        extension Foo {
+          func foo() {
+            print("Hello world!")
+          }
+
+          func bar() {
+            print("Hello world!")
+          }
+        }
+
+        struct Bar {
+          func foo() {}
+        }
+        """
+    )
+  }
+
+  func testMoveNestedFromStruct() throws {
+    try assertMoveMembersToExtension(
+      """
+      struct Outer {1️⃣
+        struct Inner {
+          func moveThis() {}
+        }2️⃣
+      }
+      """,
+      expected:
+        """
+        struct Outer {
+          struct Inner {}
+        }
+
+        extension Outer.Inner {
+          func moveThis() {}
+        }
+        """
+    )
+  }
+
+  func testMoveNestedFromStruct2() throws {
+    try assertMoveMembersToExtension(
+      """
+      struct Outer<T> {1️⃣
+        struct Inner {
+          func moveThis() {}
+        }2️⃣
+      }
+      """,
+      expected:
+        """
+        struct Outer<T> {
+          struct Inner {}
+        }
+
+        extension Outer.Inner {
+          func moveThis() {}
+        }
+        """
+    )
+  }
+
+  func testMoveNestedFunctionNameFromGeneric() throws {
+    try assertMoveMembersToExtension(
+      """
+      struct Outer<T> {
+        struct Inner {
+          func 1️⃣moveThis()2️⃣ {}
+        }
+      }
+      """,
+      expected:
+        """
+        struct Outer<T> {
+          struct Inner {}
+        }
+
+        extension Outer.Inner {
+          func moveThis() {}
+        }
+        """
+    )
+  }
+
+  func testMoveNestedFunctionName2() throws {
+    try assertMoveMembersToExtension(
+      """
+      struct Outer<T> {
+        struct Middle {
+          struct Inner {
+            func 1️⃣moveThis()2️⃣ {}
+          }
+        }
+      }
+      """,
+      expected:
+        """
+        struct Outer<T> {
+          struct Middle {
+            struct Inner {}
+          }
+        }
+
+        extension Outer.Middle.Inner {
+          func moveThis() {}
+        }
+        """
+    )
+  }
+
+  func testNestedStoredPropertyIsNotMoved() throws {
+    try assertMoveMembersToExtension(
+      """
+      struct Outer {
+        struct Inner {
+          1️⃣var value = 12️⃣
+        }
+      }
+      """,
+      expected: nil
+    )
+  }
+
+  func testNestedInvalidMemberRemains() throws {
+    try assertMoveMembersToExtension(
+      """
+      struct Outer {
+        struct Inner {1️⃣
+          var value = 1
+
+          func moveThis() {}2️⃣
+        }
+      }
+      """,
+      expected:
+        """
+        struct Outer {
+          struct Inner {
+            var value = 1
+          }
+        }
+
+        extension Outer.Inner {
+          func moveThis() {}
+        }
+        """
+    )
+  }
+
+  func testSelectedDeinitializerMember() async throws {
+    try assertMoveMembersToExtension(
+      """
+      class Foo {
+        func foo() {
+          print("Hello world!")
+        }
+
+      1️⃣deinit() {}2️⃣
+
+        func bar() {
+          print("Hello world!")
+        }
+      }
+
+      struct Bar {
+        func foo() {}
+      }
+      """,
+      expected: nil
+    )
+  }
+
+  func testMoveEmptySelection() throws {
+    try assertMoveMembersToExtension(
+      """
+      class Foo {
+        func foo() {
+          print("Hello world!")
+        }
+      1️⃣2️⃣
+        func bar() {
+          print("Hello world!")
+        }
+      }
+
+      struct Bar {
+        func foo() {}
+      }
+      """,
+      expected: nil
+    )
+  }
+}
+
+private func assertMoveMembersToExtension(
+  _ source: String,
+  expected: SourceFileSyntax?,
+  file: StaticString = #filePath,
+  line: UInt = #line
+) throws {
+  let (markers, source) = extractMarkers(source.description)
+  let positions = markers.mapValues { $0 }
+  var parser = Parser(source)
+  let tree = SourceFileSyntax.parse(from: &parser)
+
+  let range = try XCTUnwrap(positions["1️⃣"])..<XCTUnwrap(positions["2️⃣"])
+  let context = MoveMembersToExtension.Context(range: range)
+
+  try assertRefactor(
+    tree,
+    context: context,
+    provider: MoveMembersToExtension.self,
+    expected: expected,
+    file: file,
+    line: line
+  )
+}