diff --git a/app/helpers/system_note_helper.rb b/app/helpers/system_note_helper.rb
index 209bd56b78ac0ad2d82a54b4bb4090d98aefbebc..08fd97cd0481566dee8f38ea8167abe02127c124 100644
--- a/app/helpers/system_note_helper.rb
+++ b/app/helpers/system_note_helper.rb
@@ -18,7 +18,8 @@ module SystemNoteHelper
     'milestone' => 'icon_clock_o',
     'discussion' => 'icon_comment_o',
     'moved' => 'icon_arrow_circle_o_right',
-    'outdated' => 'icon_edit'
+    'outdated' => 'icon_edit',
+    'duplicate' => 'icon_clone'
   }.freeze
 
   def icon_for_system_note(note)
diff --git a/app/services/issuable_base_service.rb b/app/services/issuable_base_service.rb
index f57fbaca83654a7e2e33003d6880a6b32ccd34f0..ea4977291153c9668c8e5161b17aa9a8197e2307 100644
--- a/app/services/issuable_base_service.rb
+++ b/app/services/issuable_base_service.rb
@@ -46,10 +46,6 @@ class IssuableBaseService < BaseService
     SystemNoteService.change_time_spent(issuable, issuable.project, current_user)
   end
 
-  def create_issue_duplicate_note(issuable, original_issue)
-    SystemNoteService.mark_duplicate_issue(issuable, issuable.project, current_user, original_issue)
-  end
-
   def filter_params(issuable)
     ability_name = :"admin_#{issuable.to_ability_name}"
 
@@ -62,7 +58,7 @@ class IssuableBaseService < BaseService
       params.delete(:assignee_ids)
       params.delete(:assignee_id)
       params.delete(:due_date)
-      params.delete(:original_issue_id)
+      params.delete(:canonical_issue_id)
     end
 
     filter_assignee(issuable)
@@ -214,7 +210,6 @@ class IssuableBaseService < BaseService
     change_state(issuable)
     change_subscription(issuable)
     change_todo(issuable)
-    change_issue_duplicate(issuable)
     toggle_award(issuable)
     filter_params(issuable)
     old_labels = issuable.labels.to_a
@@ -297,22 +292,6 @@ class IssuableBaseService < BaseService
     end
   end
 
-  def change_issue_duplicate(issuable)
-    original_issue_id = params.delete(:original_issue_id)
-    return unless original_issue_id
-
-    begin
-      original_issue = IssuesFinder.new(current_user).find(original_issue_id)
-    rescue ActiveRecord::RecordNotFound
-      return
-    end
-
-    note = create_issue_duplicate_note(issuable, original_issue)
-    note.create_cross_references!
-    close_service.new(project, current_user, {}).execute(issuable)
-    original_issue.create_award_emoji(AwardEmoji::UPVOTE_NAME, issuable.author)
-  end
-
   def toggle_award(issuable)
     award = params.delete(:emoji_award)
     if award
diff --git a/app/services/issues/base_service.rb b/app/services/issues/base_service.rb
index 34199eb5d1373347188ad664d01a17eb84eaa29c..4c198fc96eaa7205bff45ea4f7d7dbd077310540 100644
--- a/app/services/issues/base_service.rb
+++ b/app/services/issues/base_service.rb
@@ -7,6 +7,14 @@ module Issues
       issue_data
     end
 
+    def reopen_service
+      Issues::ReopenService
+    end
+
+    def close_service
+      Issues::CloseService
+    end
+
     private
 
     def create_assignee_note(issue, old_assignees)
diff --git a/app/services/issues/duplicate_service.rb b/app/services/issues/duplicate_service.rb
new file mode 100644
index 0000000000000000000000000000000000000000..5c0854e664d219790e4a1495fc1e61fb7d73b282
--- /dev/null
+++ b/app/services/issues/duplicate_service.rb
@@ -0,0 +1,24 @@
+module Issues
+  class DuplicateService < Issues::BaseService
+    def execute(duplicate_issue, canonical_issue)
+      return if canonical_issue == duplicate_issue
+      return unless can?(current_user, :update_issue, duplicate_issue)
+      return unless can?(current_user, :create_note, canonical_issue)
+
+      create_issue_duplicate_note(duplicate_issue, canonical_issue)
+      create_issue_canonical_note(canonical_issue, duplicate_issue)
+
+      close_service.new(project, current_user, {}).execute(duplicate_issue)
+    end
+
+    private
+
+    def create_issue_duplicate_note(duplicate_issue, canonical_issue)
+      SystemNoteService.mark_duplicate_issue(duplicate_issue, duplicate_issue.project, current_user, canonical_issue)
+    end
+
+    def create_issue_canonical_note(canonical_issue, duplicate_issue)
+      SystemNoteService.mark_canonical_issue_of_duplicate(canonical_issue, canonical_issue.project, current_user, duplicate_issue)
+    end
+  end
+end
diff --git a/app/services/issues/update_service.rb b/app/services/issues/update_service.rb
index cd9f9a4a16e02724961b0d6384e4733336650d1c..8d918ccc635ec2ebb286575a7b39cd1e9217068e 100644
--- a/app/services/issues/update_service.rb
+++ b/app/services/issues/update_service.rb
@@ -5,6 +5,7 @@ module Issues
     def execute(issue)
       handle_move_between_iids(issue)
       filter_spam_check_params
+      change_issue_duplicate(issue)
       update(issue)
     end
 
@@ -53,14 +54,6 @@ module Issues
       end
     end
 
-    def reopen_service
-      Issues::ReopenService
-    end
-
-    def close_service
-      Issues::CloseService
-    end
-
     def handle_move_between_iids(issue)
       return unless params[:move_between_iids]
 
@@ -72,6 +65,15 @@ module Issues
       issue.move_between(issue_before, issue_after)
     end
 
+    def change_issue_duplicate(issue)
+      canonical_issue_id = params.delete(:canonical_issue_id)
+      canonical_issue = IssuesFinder.new(current_user).find_by(id: canonical_issue_id)
+
+      if canonical_issue
+        Issues::DuplicateService.new(project, current_user).execute(issue, canonical_issue)
+      end
+    end
+
     private
 
     def get_issue_if_allowed(project, iid)
diff --git a/app/services/quick_actions/interpret_service.rb b/app/services/quick_actions/interpret_service.rb
index 3eecf0b5545c86381c1ea4de38246748c0aa50b8..5dc1b91d2c0486a67b682e113e691604bdb35528 100644
--- a/app/services/quick_actions/interpret_service.rb
+++ b/app/services/quick_actions/interpret_service.rb
@@ -472,6 +472,9 @@ module QuickActions
     end
 
     desc 'Mark this issue as a duplicate of another issue'
+    explanation do |duplicate_reference|
+      "Marks this issue as a duplicate of #{duplicate_reference}."
+    end
     params '#issue'
     condition do
       issuable.is_a?(Issue) &&
@@ -479,9 +482,10 @@ module QuickActions
         current_user.can?(:"update_#{issuable.to_ability_name}", issuable)
     end
     command :duplicate do |duplicate_param|
-      original_issue = extract_references(duplicate_param, :issue).first
-      if original_issue.present? && original_issue != issuable
-        @updates[:original_issue_id] = original_issue.id
+      canonical_issue = extract_references(duplicate_param, :issue).first
+
+      if canonical_issue.present?
+        @updates[:canonical_issue_id] = canonical_issue.id
       end
     end
 
diff --git a/app/services/system_note_service.rb b/app/services/system_note_service.rb
index ed079f0e495f58221f9c213b055abb617c27d8b7..2dbee9c246e270a9e43913bae312465bdcde96a5 100644
--- a/app/services/system_note_service.rb
+++ b/app/services/system_note_service.rb
@@ -554,10 +554,10 @@ module SystemNoteService
 
   # Called when a Noteable has been marked as a duplicate of another Issue
   #
-  # noteable       - Noteable object
-  # project        - Project owning noteable
-  # author         - User performing the change
-  # original_issue - Issue that this is a duplicate of
+  # noteable        - Noteable object
+  # project         - Project owning noteable
+  # author          - User performing the change
+  # canonical_issue - Issue that this is a duplicate of
   #
   # Example Note text:
   #
@@ -566,8 +566,27 @@ module SystemNoteService
   #   "marked this issue as a duplicate of other_project#5678"
   #
   # Returns the created Note object
-  def mark_duplicate_issue(noteable, project, author, original_issue)
-    body = "marked this issue as a duplicate of #{original_issue.to_reference(project)}"
+  def mark_duplicate_issue(noteable, project, author, canonical_issue)
+    body = "marked this issue as a duplicate of #{canonical_issue.to_reference(project)}"
+    create_note(NoteSummary.new(noteable, project, author, body, action: 'duplicate'))
+  end
+
+  # Called when a Noteable has been marked as the canonical Issue of a duplicate
+  #
+  # noteable        - Noteable object
+  # project         - Project owning noteable
+  # author          - User performing the change
+  # duplicate_issue - Issue that was a duplicate of this
+  #
+  # Example Note text:
+  #
+  #   "marked #1234 as a duplicate of this issue"
+  #
+  #   "marked other_project#5678 as a duplicate of this issue"
+  #
+  # Returns the created Note object
+  def mark_canonical_issue_of_duplicate(noteable, project, author, duplicate_issue)
+    body = "marked #{duplicate_issue.to_reference(project)} as a duplicate of this issue"
     create_note(NoteSummary.new(noteable, project, author, body, action: 'duplicate'))
   end
 
diff --git a/app/views/shared/icons/_icon_clone.svg b/app/views/shared/icons/_icon_clone.svg
new file mode 100644
index 0000000000000000000000000000000000000000..ccc897aa98f834d65d0865639a98bbb6b6ecc058
--- /dev/null
+++ b/app/views/shared/icons/_icon_clone.svg
@@ -0,0 +1,3 @@
+<svg version="1.1" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" width="14" height="14" viewBox="0 0 14 14">
+<path d="M13 12.75v-8.5q0-0.102-0.074-0.176t-0.176-0.074h-8.5q-0.102 0-0.176 0.074t-0.074 0.176v8.5q0 0.102 0.074 0.176t0.176 0.074h8.5q0.102 0 0.176-0.074t0.074-0.176zM14 4.25v8.5q0 0.516-0.367 0.883t-0.883 0.367h-8.5q-0.516 0-0.883-0.367t-0.367-0.883v-8.5q0-0.516 0.367-0.883t0.883-0.367h8.5q0.516 0 0.883 0.367t0.367 0.883zM11 1.25v1.25h-1v-1.25q0-0.102-0.074-0.176t-0.176-0.074h-8.5q-0.102 0-0.176 0.074t-0.074 0.176v8.5q0 0.102 0.074 0.176t0.176 0.074h1.25v1h-1.25q-0.516 0-0.883-0.367t-0.367-0.883v-8.5q0-0.516 0.367-0.883t0.883-0.367h8.5q0.516 0 0.883 0.367t0.367 0.883z"></path>
+</svg>
diff --git a/changelogs/unreleased/26372-duplicate-issue-slash-command.yml b/changelogs/unreleased/26372-duplicate-issue-slash-command.yml
index 079ebe59f98a445eceacbb3cb4d160223f3a159f..3108344e0bf7a3311c7db3d7582a959eb84cffe0 100644
--- a/changelogs/unreleased/26372-duplicate-issue-slash-command.yml
+++ b/changelogs/unreleased/26372-duplicate-issue-slash-command.yml
@@ -1,4 +1,4 @@
 ---
-title: Added /duplicate slash command to close a duplicate issue
-merge_request:
+title: Added /duplicate quick action to close a duplicate issue
+merge_request: 12845
 author: Ryan Scott
diff --git a/spec/services/issues/duplicate_service_spec.rb b/spec/services/issues/duplicate_service_spec.rb
new file mode 100644
index 0000000000000000000000000000000000000000..82daf53b1737110165be376f43033c8873b4e7e9
--- /dev/null
+++ b/spec/services/issues/duplicate_service_spec.rb
@@ -0,0 +1,80 @@
+require 'spec_helper'
+
+describe Issues::DuplicateService, services: true do
+  let(:user) { create(:user) }
+  let(:canonical_project) { create(:empty_project) }
+  let(:duplicate_project) { create(:empty_project) }
+
+  let(:canonical_issue) { create(:issue, project: canonical_project) }
+  let(:duplicate_issue) { create(:issue, project: duplicate_project) }
+
+  subject { described_class.new(duplicate_project, user, {}) }
+
+  describe '#execute' do
+    context 'when the issues passed are the same' do
+      it 'does nothing' do
+        expect(subject).not_to receive(:close_service)
+        expect(SystemNoteService).not_to receive(:mark_duplicate_issue)
+        expect(SystemNoteService).not_to receive(:mark_canonical_issue_of_duplicate)
+
+        subject.execute(duplicate_issue, duplicate_issue)
+      end
+    end
+
+    context 'when the user cannot update the duplicate issue' do
+      before do
+        canonical_project.add_reporter(user)
+      end
+
+      it 'does nothing' do
+        expect(subject).not_to receive(:close_service)
+        expect(SystemNoteService).not_to receive(:mark_duplicate_issue)
+        expect(SystemNoteService).not_to receive(:mark_canonical_issue_of_duplicate)
+
+        subject.execute(duplicate_issue, canonical_issue)
+      end
+    end
+
+    context 'when the user cannot comment on the canonical issue' do
+      before do
+        duplicate_project.add_reporter(user)
+      end
+
+      it 'does nothing' do
+        expect(subject).not_to receive(:close_service)
+        expect(SystemNoteService).not_to receive(:mark_duplicate_issue)
+        expect(SystemNoteService).not_to receive(:mark_canonical_issue_of_duplicate)
+
+        subject.execute(duplicate_issue, canonical_issue)
+      end
+    end
+
+    context 'when the user can mark the issue as a duplicate' do
+      before do
+        canonical_project.add_reporter(user)
+        duplicate_project.add_reporter(user)
+      end
+
+      it 'closes the duplicate issue' do
+        subject.execute(duplicate_issue, canonical_issue)
+
+        expect(duplicate_issue.reload).to be_closed
+        expect(canonical_issue.reload).to be_open
+      end
+
+      it 'adds a system note to the duplicate issue' do
+        expect(SystemNoteService)
+          .to receive(:mark_duplicate_issue).with(duplicate_issue, duplicate_project, user, canonical_issue)
+
+        subject.execute(duplicate_issue, canonical_issue)
+      end
+
+      it 'adds a system note to the canonical issue' do
+        expect(SystemNoteService)
+          .to receive(:mark_canonical_issue_of_duplicate).with(canonical_issue, canonical_project, user, duplicate_issue)
+
+        subject.execute(duplicate_issue, canonical_issue)
+      end
+    end
+  end
+end
diff --git a/spec/services/issues/update_service_spec.rb b/spec/services/issues/update_service_spec.rb
index e7f3ab93395c69c3ea1f942efae55139a5898393..064be940a1c889046436179827a3bff0b6b7f88c 100644
--- a/spec/services/issues/update_service_spec.rb
+++ b/spec/services/issues/update_service_spec.rb
@@ -492,43 +492,22 @@ describe Issues::UpdateService, services: true do
     end
 
     context 'duplicate issue' do
-      let(:original_issue) { create(:issue, project: project) }
+      let(:canonical_issue) { create(:issue, project: project) }
 
-      context 'invalid original_issue_id' do
-        before do
-          update_issue(original_issue_id: 123456789)
-        end
-
-        it 'does not close the issue' do
-          expect(issue.reload).not_to be_closed
-        end
+      context 'invalid canonical_issue_id' do
+        it 'does not call the duplicate service' do
+          expect(Issues::DuplicateService).not_to receive(:new)
 
-        it 'does not create a system note' do
-          note = find_note("marked this issue as a duplicate of #{original_issue.to_reference}")
-          expect(note).to be_nil
-        end
-
-        it 'does not upvote the issue on behalf of the author' do
-          expect(original_issue).not_to be_awarded_emoji(AwardEmoji::UPVOTE_NAME, issue.author)
+          update_issue(canonical_issue_id: 123456789)
         end
       end
 
-      context 'valid original_issue_id' do
-        before do
-          update_issue(original_issue_id: original_issue.id)
-        end
-
-        it 'closes the issue' do
-          expect(issue.reload).to be_closed
-        end
-
-        it 'creates a system note that this issue is a duplicate' do
-          note = find_note("marked this issue as a duplicate of #{original_issue.to_reference}")
-          expect(note).not_to be_nil
-        end
+      context 'valid canonical_issue_id' do
+        it 'calls the duplicate service with both issues' do
+          expect_any_instance_of(Issues::DuplicateService)
+            .to receive(:execute).with(issue, canonical_issue)
 
-        it 'upvotes the issue on behalf of the author' do
-          expect(original_issue).to be_awarded_emoji(AwardEmoji::UPVOTE_NAME, issue.author)
+          update_issue(canonical_issue_id: canonical_issue.id)
         end
       end
     end
diff --git a/spec/services/quick_actions/interpret_service_spec.rb b/spec/services/quick_actions/interpret_service_spec.rb
index 1d60b74e566f5b5703060b7a27379fd6eeafc4f2..2a2a5c38e4beca53b7fa8e5852134f9bc22e092d 100644
--- a/spec/services/quick_actions/interpret_service_spec.rb
+++ b/spec/services/quick_actions/interpret_service_spec.rb
@@ -262,11 +262,11 @@ describe QuickActions::InterpretService, services: true do
     end
 
     shared_examples 'duplicate command' do
-      it 'fetches issue and populates original_issue_id if content contains /duplicate issue_reference' do
+      it 'fetches issue and populates canonical_issue_id if content contains /duplicate issue_reference' do
         issue_duplicate # populate the issue
         _, updates = service.execute(content, issuable)
 
-        expect(updates).to eq(original_issue_id: issue_duplicate.id)
+        expect(updates).to eq(canonical_issue_id: issue_duplicate.id)
       end
     end
 
@@ -660,11 +660,6 @@ describe QuickActions::InterpretService, services: true do
         let(:issuable) { issue }
       end
 
-      it_behaves_like 'empty command' do
-        let(:content) { "/duplicate #{issue.to_reference}" }
-        let(:issuable) { issue }
-      end
-
       it_behaves_like 'empty command' do
         let(:content) { '/duplicate' }
         let(:issuable) { issue }
@@ -679,7 +674,7 @@ describe QuickActions::InterpretService, services: true do
         end
 
         it_behaves_like 'empty command' do
-          let(:content) { '/duplicate imaginary#1234' }
+          let(:content) { "/duplicate imaginary#1234" }
           let(:issuable) { issue }
         end
 
diff --git a/spec/services/system_note_service_spec.rb b/spec/services/system_note_service_spec.rb
index db1208891195035cd0a1287cb1152b00a7e855c3..681b419aedfbb561058d8cf6e5ebed5e18dd4e20 100644
--- a/spec/services/system_note_service_spec.rb
+++ b/spec/services/system_note_service_spec.rb
@@ -1103,27 +1103,52 @@ describe SystemNoteService, services: true do
   end
 
   describe '.mark_duplicate_issue' do
-    subject { described_class.mark_duplicate_issue(noteable, project, author, original_issue) }
+    subject { described_class.mark_duplicate_issue(noteable, project, author, canonical_issue) }
 
     context 'within the same project' do
-      let(:original_issue) { create(:issue, project: project) }
+      let(:canonical_issue) { create(:issue, project: project) }
 
       it_behaves_like 'a system note' do
         let(:action) { 'duplicate' }
       end
 
-      it { expect(subject.note).to eq "marked this issue as a duplicate of #{original_issue.to_reference}" }
+      it { expect(subject.note).to eq "marked this issue as a duplicate of #{canonical_issue.to_reference}" }
     end
 
     context 'across different projects' do
       let(:other_project)  { create(:empty_project) }
-      let(:original_issue) { create(:issue, project: other_project) }
+      let(:canonical_issue) { create(:issue, project: other_project) }
 
       it_behaves_like 'a system note' do
         let(:action) { 'duplicate' }
       end
 
-      it { expect(subject.note).to eq "marked this issue as a duplicate of #{original_issue.to_reference(project)}" }
+      it { expect(subject.note).to eq "marked this issue as a duplicate of #{canonical_issue.to_reference(project)}" }
+    end
+  end
+
+  describe '.mark_canonical_issue_of_duplicate' do
+    subject { described_class.mark_canonical_issue_of_duplicate(noteable, project, author, duplicate_issue) }
+
+    context 'within the same project' do
+      let(:duplicate_issue) { create(:issue, project: project) }
+
+      it_behaves_like 'a system note' do
+        let(:action) { 'duplicate' }
+      end
+
+      it { expect(subject.note).to eq "marked #{duplicate_issue.to_reference} as a duplicate of this issue" }
+    end
+
+    context 'across different projects' do
+      let(:other_project)  { create(:empty_project) }
+      let(:duplicate_issue) { create(:issue, project: other_project) }
+
+      it_behaves_like 'a system note' do
+        let(:action) { 'duplicate' }
+      end
+
+      it { expect(subject.note).to eq "marked #{duplicate_issue.to_reference(project)} as a duplicate of this issue" }
     end
   end
 end