diff --git a/Gemfile b/Gemfile
index 0dd0555d66d4..c064b972448e 100644
--- a/Gemfile
+++ b/Gemfile
@@ -14,6 +14,7 @@ gem 'rspec', '~> 3.7'
 gem 'rubocop-performance', '~> 1.23.0'
 gem 'rubocop-rake', '~> 0.6.0'
 gem 'rubocop-rspec', '~> 3.3.0'
+gem 'ruby-lsp', '~> 0.17'
 gem 'simplecov', '~> 0.20'
 gem 'stackprof', platform: :mri
 gem 'test-queue'
diff --git a/changelog/new_support_ruby_lsp_addon.md b/changelog/new_support_ruby_lsp_addon.md
new file mode 100644
index 000000000000..e20f7a212dd5
--- /dev/null
+++ b/changelog/new_support_ruby_lsp_addon.md
@@ -0,0 +1 @@
+* [#13628](https://github.com/rubocop/rubocop/pull/13628): Add support for Ruby LSP as a built-in add-on. ([@koic][])
diff --git a/lib/ruby_lsp/rubocop/addon.rb b/lib/ruby_lsp/rubocop/addon.rb
new file mode 100644
index 000000000000..9d919f091d4e
--- /dev/null
+++ b/lib/ruby_lsp/rubocop/addon.rb
@@ -0,0 +1,73 @@
+# frozen_string_literal: true
+
+require_relative '../../rubocop'
+require_relative '../../rubocop/lsp/logger'
+require_relative 'wraps_built_in_lsp_runtime'
+
+module RubyLsp
+  module RuboCop
+    # A Ruby LSP add-on for RuboCop.
+    class Addon < RubyLsp::Addon
+      def initializer
+        @wraps_built_in_lsp_runtime = nil
+      end
+
+      def name
+        'RuboCop'
+      end
+
+      def activate(global_state, message_queue)
+        ::RuboCop::LSP::Logger.log("Activating RuboCop LSP addon #{::RuboCop::Version::STRING}.")
+
+        @wraps_built_in_lsp_runtime = WrapsBuiltinLspRuntime.new
+
+        global_state.register_formatter('rubocop', @wraps_built_in_lsp_runtime)
+
+        register_additional_file_watchers(global_state, message_queue)
+
+        ::RuboCop::LSP::Logger.log("Initialized RuboCop LSP addon #{::RuboCop::Version::STRING}.")
+      end
+
+      def deactivate
+        @wraps_built_in_lsp_runtime = nil
+      end
+
+      # rubocop:disable Layout/LineLength, Metrics/MethodLength
+      def register_additional_file_watchers(global_state, message_queue)
+        return unless global_state.supports_watching_files
+
+        message_queue << Request.new(
+          id: 'rubocop-file-watcher',
+          method: 'client/registerCapability',
+          params: Interface::RegistrationParams.new(
+            registrations: [
+              Interface::Registration.new(
+                id: 'workspace/didChangeWatchedFilesRuboCop',
+                method: 'workspace/didChangeWatchedFiles',
+                register_options: Interface::DidChangeWatchedFilesRegistrationOptions.new(
+                  watchers: [
+                    Interface::FileSystemWatcher.new(
+                      glob_pattern: '**/.rubocop.yml',
+                      kind: Constant::WatchKind::CREATE | Constant::WatchKind::CHANGE | Constant::WatchKind::DELETE
+                    )
+                  ]
+                )
+              )
+            ]
+          )
+        )
+      end
+      # rubocop:enable Layout/LineLength, Metrics/MethodLength
+
+      def workspace_did_change_watched_files(changes)
+        return unless changes.any? { |change| change[:uri].end_with?('.rubocop.yml') }
+
+        @wraps_built_in_lsp_runtime.init!
+
+        ::RuboCop::LSP::Logger(<<~MESSAGE)
+          Re-initialized RuboCop LSP addon #{::RuboCop::Version::STRING} due to .rubocop.yml file change.
+        MESSAGE
+      end
+    end
+  end
+end
diff --git a/lib/ruby_lsp/rubocop/wraps_built_in_lsp_runtime.rb b/lib/ruby_lsp/rubocop/wraps_built_in_lsp_runtime.rb
new file mode 100644
index 000000000000..0274b1f6ff25
--- /dev/null
+++ b/lib/ruby_lsp/rubocop/wraps_built_in_lsp_runtime.rb
@@ -0,0 +1,107 @@
+# frozen_string_literal: true
+
+module RubyLsp
+  module RuboCop
+    # Wrap RuboCop's built-in runtime for Ruby LSP's add-on.
+    class WrapsBuiltinLspRuntime
+      include RubyLsp::Requests::Support::Formatter
+
+      def initialize
+        init!
+      end
+
+      def init!
+        config = ::RuboCop::ConfigStore.new
+        @runtime = ::RuboCop::LSP::Runtime.new(config)
+        @rubocop_config = config.for_pwd
+        @cop_registry = ::RuboCop::Cop::Registry.global.to_h
+      end
+
+      # rubocop:disable Metrics/AbcSize, Metrics/MethodLength
+      def run_diagnostic(uri, document)
+        offenses = @runtime.offenses(uri_to_path(uri), document.source)
+
+        # rubocop:disable Metrics/BlockLength
+        offenses.map do |o|
+          cop_name = o[:cop_name]
+
+          msg = o[:message].delete_prefix(cop_name)
+          loc = o[:location]
+
+          severity = case o[:severity]
+                     when 'error', 'fatal'
+                       RubyLsp::Constant::DiagnosticSeverity::ERROR
+                     when 'warning'
+                       RubyLsp::Constant::DiagnosticSeverity::WARNING
+                     when 'convention'
+                       RubyLsp::Constant::DiagnosticSeverity::INFORMATION
+                     when 'refactor', 'info'
+                       RubyLsp::Constant::DiagnosticSeverity::HINT
+                     else # the above cases fully cover what RuboCop sends at this time
+                       logger.puts "Unknown severity: #{severity.inspect}"
+                       RubyLsp::Constant::DiagnosticSeverity::HINT
+                     end
+
+          RubyLsp::Interface::Diagnostic.new(
+            code: cop_name,
+            code_description: code_description(cop_name),
+            message: msg,
+            source: 'RuboCop',
+            severity: severity,
+            range: RubyLsp::Interface::Range.new(
+              start: RubyLsp::Interface::Position.new(
+                line: loc[:start_line] - 1, character: loc[:start_column] - 1
+              ),
+
+              end: RubyLsp::Interface::Position.new(
+                line: loc[:last_line] - 1, character: loc[:last_column]
+              )
+            )
+            # TODO: We need to do something like to support quickfixes thru code actions
+            # See: https://github.com/Shopify/ruby-lsp/blob/4c1906172add4d5c39c35d3396aa29c768bfb898/lib/ruby_lsp/requests/support/rubocop_diagnostic.rb#L62
+            # data: {
+            #   correctable: correctable?(offense),
+            #   code_actions: to_lsp_code_actions
+            # }
+            #
+            # Right now, our offenses are all just JSON parsed from stdout shelling to RuboCop, so
+            # it seems we don't have the corrector available to us.
+            #
+            # Lifted from:
+            # https://github.com/Shopify/ruby-lsp/blob/8d4c17efce4e8ecc8e7c557ab2981db6b22c0b6d/lib/ruby_lsp/requests/support/rubocop_diagnostic.rb#L201
+            # def correctable?(offense)
+            #   !offense.corrector.nil?
+            # end
+          )
+        end
+        # rubocop:enable Metrics/BlockLength
+      end
+      # rubocop:enable Metrics/AbcSize, Metrics/MethodLength
+
+      def run_formatting(uri, document)
+        @runtime.format(uri_to_path(uri), document.source, command: 'rubocop.formatAutocorrects')
+      end
+
+      private
+
+      # duplicated from: lib/standard/lsp/routes.rb
+      # modified to incorporate Ruby LSP's to_standardized_path method
+      def uri_to_path(uri)
+        if uri.respond_to?(:to_standardized_path) && (standardized_path = uri.to_standardized_path)
+          standardized_path
+        else
+          uri.to_s.delete_prefix('file://')
+        end
+      end
+
+      # lifted from:
+      # https://github.com/Shopify/ruby-lsp/blob/4c1906172add4d5c39c35d3396aa29c768bfb898/lib/ruby_lsp/requests/support/rubocop_diagnostic.rb#L84
+      def code_description(cop_name)
+        return unless (cop_class = @cop_registry[cop_name]&.first)
+        return unless (doc_url = cop_class.documentation_url(@rubocop_config))
+
+        Interface::CodeDescription.new(href: doc_url)
+      end
+    end
+  end
+end
diff --git a/spec/fixtures/ruby_lsp/example.rb b/spec/fixtures/ruby_lsp/example.rb
new file mode 100644
index 000000000000..1110d83a7217
--- /dev/null
+++ b/spec/fixtures/ruby_lsp/example.rb
@@ -0,0 +1,2 @@
+s = 'hi'
+puts s
diff --git a/spec/ruby_lsp/rubocop/addon_spec.rb b/spec/ruby_lsp/rubocop/addon_spec.rb
new file mode 100644
index 000000000000..2324984f5df8
--- /dev/null
+++ b/spec/ruby_lsp/rubocop/addon_spec.rb
@@ -0,0 +1,151 @@
+# frozen_string_literal: true
+
+require 'ruby_lsp/internal'
+require 'ruby_lsp/rubocop/addon'
+
+describe 'RubyLSP::RuboCop::Addon', :isolated_environment, :lsp do
+  let(:addon) do
+    RubyLsp::RuboCop::Addon.new
+  end
+
+  let(:source) do
+    <<~RUBY
+      s = "hello"
+      puts s
+    RUBY
+  end
+
+  before do
+    # Suppress Ruby LSP's add-on logging.
+    allow(RuboCop::LSP::Logger).to receive(:log)
+  end
+
+  describe 'Add-on name' do
+    it 'is RuboCop' do
+      expect(addon.name).to eq 'RuboCop'
+    end
+  end
+
+  describe 'textDocument/diagnostic' do
+    subject(:result) do
+      with_server(source, 'example.rb') do |server, uri|
+        server.process_message(
+          id: 2,
+          method: 'textDocument/diagnostic',
+          params: {
+            textDocument: {
+              uri: uri
+            }
+          }
+        )
+
+        server.pop_response
+      end
+    end
+
+    let(:first_item) { result.response.items.first }
+    let(:second_item) { result.response.items[1] }
+
+    it 'has basic result information' do
+      expect(result).to be_an_instance_of(RubyLsp::Result)
+      expect(result.response.kind).to eq 'full'
+      expect(result.response.items.size).to eq 2
+    end
+
+    it 'has first diagnostic information' do
+      expect(first_item.range.start.to_hash).to eq({ line: 0, character: 0 })
+      expect(first_item.range.end.to_hash).to eq({ line: 0, character: 1 })
+      expect(first_item.severity).to eq RubyLsp::Constant::DiagnosticSeverity::INFORMATION
+      expect(first_item.code).to eq 'Style/FrozenStringLiteralComment'
+      expect(first_item.code_description.href).to eq 'https://docs.rubocop.org/rubocop/cops_style.html#stylefrozenstringliteralcomment'
+      expect(first_item.source).to eq 'RuboCop'
+      expect(first_item.message).to eq 'Missing frozen string literal comment.'
+    end
+
+    it 'has second diagnostic information' do
+      second_item = result.response.items[1]
+      expect(second_item.range.start.to_hash).to eq({ line: 0, character: 4 })
+      expect(second_item.range.end.to_hash).to eq({ line: 0, character: 11 })
+      expect(second_item.severity).to eq RubyLsp::Constant::DiagnosticSeverity::INFORMATION
+      expect(second_item.code).to eq 'Style/StringLiterals'
+      expect(second_item.code_description.href).to eq 'https://docs.rubocop.org/rubocop/cops_style.html#stylestringliterals'
+      expect(second_item.source).to eq 'RuboCop'
+      expect(second_item.message).to eq <<~MESSAGE.chop
+        Prefer single-quoted strings when you don't need string interpolation or special symbols.
+      MESSAGE
+    end
+  end
+
+  describe 'textDocument/formatting' do
+    subject(:result) do
+      with_server(source, 'example.rb') do |server, uri|
+        server.process_message(
+          id: 2,
+          method: 'textDocument/formatting',
+          params: {
+            textDocument: { uri: uri },
+            position: { line: 0, character: 0 }
+          }
+        )
+
+        server.pop_response
+      end
+    end
+
+    it 'has basic result information' do
+      expect(result).to be_an_instance_of(RubyLsp::Result)
+      expect(result.response.size).to eq 1
+    end
+
+    it 'has autocorrected code' do
+      expect(result.response.first.new_text).to eq <<~RUBY
+        s = 'hello'
+        puts s
+      RUBY
+    end
+  end
+
+  private
+
+  # Lifted from here, because we need to override the formatter to RuboCop in the spec helper:
+  # https://github.com/Shopify/ruby-lsp/blob/4c1906172add4d5c39c35d3396aa29c768bfb898/lib/ruby_lsp/test_helper.rb#L20
+  #
+  # rubocop:disable Metrics/AbcSize, Metrics/MethodLength
+  def with_server(
+    source = nil, path = 'fake.rb', pwd: '..', stub_no_typechecker: false, load_addons: true
+  )
+    Dir.chdir(pwd) do
+      server = RubyLsp::Server.new(test_mode: true)
+      uri = URI(File.join(server.global_state.workspace_path, path))
+      server.global_state.formatter = 'rubocop'
+      server.global_state.instance_variable_set(:@linters, ['rubocop'])
+      server.global_state.stubs(:typechecker).returns(false) if stub_no_typechecker
+
+      if source
+        server.process_message(
+          method: 'textDocument/didOpen',
+          params: {
+            textDocument: {
+              uri: uri,
+              text: source,
+              version: 1
+            }
+          }
+        )
+      end
+
+      server.global_state.index.index_single(
+        RubyIndexer::IndexablePath.new(nil, uri.to_standardized_path), source
+      )
+      server.load_addons if load_addons
+
+      yield server, uri
+    end
+  ensure
+    if load_addons
+      RubyLsp::Addon.addons.each(&:deactivate)
+      RubyLsp::Addon.addons.clear
+    end
+  end
+  # rubocop:enable Metrics/AbcSize, Metrics/MethodLength
+end