diff --git a/actiontext/CHANGELOG.md b/actiontext/CHANGELOG.md
index 393daabfa3..3e97ffb0d6 100644
--- a/actiontext/CHANGELOG.md
+++ b/actiontext/CHANGELOG.md
@@ -1,3 +1,16 @@
+*   Declare `ActionText::FixtureSet.attachment` to generate an
+    `<action-text-attachment sgid="..."></action-text-attachment>` element with
+    a valid `sgid` attribute.
+
+    ```ruby
+    hello_world_review_content:
+      record: hello_world (Review)
+      name: content
+      body: <p><%= ActionText::FixtureSet.attachment("messages", :hello_world) %> is great!</p>
+    ```
+
+    *Sean Doyle*
+
 *   Locate `fill_in_rich_text_area` by `<label>` text
 
     In addition to searching for `<trix-editor>` elements with the appropriate
diff --git a/actiontext/lib/action_text.rb b/actiontext/lib/action_text.rb
index 15fdf70b3b..f7ea0fe854 100644
--- a/actiontext/lib/action_text.rb
+++ b/actiontext/lib/action_text.rb
@@ -14,6 +14,7 @@ module ActionText
   autoload :Attribute
   autoload :Content
   autoload :Fragment
+  autoload :FixtureSet
   autoload :HtmlConversion
   autoload :PlainTextConversion
   autoload :Rendering
diff --git a/actiontext/lib/action_text/fixture_set.rb b/actiontext/lib/action_text/fixture_set.rb
new file mode 100644
index 0000000000..8f3471d28a
--- /dev/null
+++ b/actiontext/lib/action_text/fixture_set.rb
@@ -0,0 +1,12 @@
+# frozen_string_literal: true
+
+module ActionText
+  class FixtureSet
+    def self.attachment(fixture_set_name, label, column_type: :integer)
+      signed_global_id = ActiveRecord::FixtureSet.signed_global_id fixture_set_name, label,
+        column_type: column_type, for: ActionText::Attachable::LOCATOR_NAME
+
+      %(<action-text-attachment sgid="#{signed_global_id}"></action-text-attachment>)
+    end
+  end
+end
diff --git a/actiontext/test/fixtures/action_text/rich_texts.yml b/actiontext/test/fixtures/action_text/rich_texts.yml
new file mode 100644
index 0000000000..8c1d7a1c2d
--- /dev/null
+++ b/actiontext/test/fixtures/action_text/rich_texts.yml
@@ -0,0 +1,4 @@
+hello_world_review_content:
+  record: hello_world (Review)
+  name: content
+  body: <p><%= ActionText::FixtureSet.attachment("messages", :hello_world) %> is great!</p>
diff --git a/actiontext/test/fixtures/messages.yml b/actiontext/test/fixtures/messages.yml
new file mode 100644
index 0000000000..696fb8a163
--- /dev/null
+++ b/actiontext/test/fixtures/messages.yml
@@ -0,0 +1,2 @@
+hello_world:
+  subject: "A greeting"
diff --git a/actiontext/test/fixtures/reviews.yml b/actiontext/test/fixtures/reviews.yml
new file mode 100644
index 0000000000..d06a8cc1dd
--- /dev/null
+++ b/actiontext/test/fixtures/reviews.yml
@@ -0,0 +1,3 @@
+hello_world:
+  message: $LABEL
+  author_name: "Ruby"
diff --git a/actiontext/test/unit/fixture_set_test.rb b/actiontext/test/unit/fixture_set_test.rb
new file mode 100644
index 0000000000..08108c27f6
--- /dev/null
+++ b/actiontext/test/unit/fixture_set_test.rb
@@ -0,0 +1,14 @@
+# frozen_string_literal: true
+
+require "test_helper"
+
+class ActionText::FixtureSetTest < ActiveSupport::TestCase
+  def test_action_text_attachment
+    message = messages(:hello_world)
+    review = reviews(:hello_world)
+
+    attachments = review.content.body.attachments
+
+    assert_includes attachments.map(&:attachable), message
+  end
+end
diff --git a/activerecord/lib/active_record/fixtures.rb b/activerecord/lib/active_record/fixtures.rb
index 4022b37dec..f2257be306 100644
--- a/activerecord/lib/active_record/fixtures.rb
+++ b/activerecord/lib/active_record/fixtures.rb
@@ -585,6 +585,14 @@ module ActiveRecord
         end
       end
 
+      def signed_global_id(fixture_set_name, label, column_type: :integer, **options)
+        identifier = identify(label, column_type)
+        model_name = default_fixture_model_name(fixture_set_name)
+        uri = URI::GID.build([GlobalID.app, model_name, identifier, {}])
+
+        SignedGlobalID.new(uri, **options)
+      end
+
       # Superclass for the evaluation contexts used by ERB fixtures.
       def context_class
         @context_class ||= Class.new
diff --git a/guides/source/6_1_release_notes.md b/guides/source/6_1_release_notes.md
index cadc237366..7e57148bdd 100644
--- a/guides/source/6_1_release_notes.md
+++ b/guides/source/6_1_release_notes.md
@@ -402,6 +402,10 @@ Please refer to the [Changelog][action-text] for detailed changes.
     editor and fill it with given HTML content.
     ([Pull Request](https://github.com/rails/rails/pull/35885))
 
+*   Add `ActionText::FixtureSet.attachment` to generate
+    `<action-text-attachment>` elements in database fixtures.
+    ([Pull Request](https://github.com/rails/rails/pull/40289))
+
 Action Mailbox
 ----------