diff --git a/changelogs/unreleased/feature--32877-add-default-field-branch-api.yml b/changelogs/unreleased/feature--32877-add-default-field-branch-api.yml
new file mode 100644
index 00000000000..a99ecc9a67e
--- /dev/null
+++ b/changelogs/unreleased/feature--32877-add-default-field-branch-api.yml
@@ -0,0 +1,5 @@
+---
+title: Add default parameter to branches API
+merge_request: 21294
+author: Riccardo Padovani
+type: changed
diff --git a/doc/api/branches.md b/doc/api/branches.md
index bfb21608d28..4abf0639eb0 100644
--- a/doc/api/branches.md
+++ b/doc/api/branches.md
@@ -27,6 +27,7 @@ Example response:
     "name": "master",
     "merged": false,
     "protected": true,
+    "default": true,
     "developers_can_push": false,
     "developers_can_merge": false,
     "can_push": true,
@@ -75,6 +76,7 @@ Example response:
   "name": "master",
   "merged": false,
   "protected": true,
+  "default": true,
   "developers_can_push": false,
   "developers_can_merge": false,
   "can_push": true,
@@ -141,6 +143,7 @@ Example response:
   "name": "master",
   "merged": false,
   "protected": true,
+  "default": true,
   "developers_can_push": true,
   "developers_can_merge": true,
   "can_push": true
@@ -190,6 +193,7 @@ Example response:
   "name": "master",
   "merged": false,
   "protected": false,
+  "default": true,
   "developers_can_push": false,
   "developers_can_merge": false,
   "can_push": true
@@ -234,6 +238,7 @@ Example response:
   "name": "newbranch",
   "merged": false,
   "protected": false,
+  "default": false,
   "developers_can_push": false,
   "developers_can_merge": false,
   "can_push": true
diff --git a/lib/api/entities.rb b/lib/api/entities.rb
index 95b25d7351a..59042d2b568 100644
--- a/lib/api/entities.rb
+++ b/lib/api/entities.rb
@@ -370,6 +370,10 @@ module API
       expose :can_push do |repo_branch, options|
         Gitlab::UserAccess.new(options[:current_user], project: options[:project]).can_push_to_branch?(repo_branch.name)
       end
+
+      expose :default do |repo_branch, options|
+        options[:project].default_branch == repo_branch.name
+      end
     end
 
     class TreeObject < Grape::Entity
diff --git a/spec/fixtures/api/schemas/public_api/v4/branch.json b/spec/fixtures/api/schemas/public_api/v4/branch.json
index a8891680d06..3b0f010bc4f 100644
--- a/spec/fixtures/api/schemas/public_api/v4/branch.json
+++ b/spec/fixtures/api/schemas/public_api/v4/branch.json
@@ -5,6 +5,7 @@
     "commit",
     "merged",
     "protected",
+    "default",
     "developers_can_push",
     "developers_can_merge"
   ],
@@ -13,6 +14,7 @@
     "commit": { "$ref": "commit/basic.json" },
     "merged": { "type": "boolean" },
     "protected": { "type": "boolean" },
+    "default": { "type": "boolean" },
     "developers_can_push": { "type": "boolean" },
     "developers_can_merge": { "type": "boolean" },
     "can_push": { "type": "boolean" }