diff --git a/src/__phutil_library_map__.php b/src/__phutil_library_map__.php
--- a/src/__phutil_library_map__.php
+++ b/src/__phutil_library_map__.php
@@ -487,6 +487,7 @@
     'DifferentialChangesetTwoUpTestRenderer' => 'applications/differential/render/DifferentialChangesetTwoUpTestRenderer.php',
     'DifferentialChangesetViewController' => 'applications/differential/controller/DifferentialChangesetViewController.php',
     'DifferentialCloseConduitAPIMethod' => 'applications/differential/conduit/DifferentialCloseConduitAPIMethod.php',
+    'DifferentialCoAuthorsCommitMessageField' => 'applications/differential/field/DifferentialCoAuthorsCommitMessageField.php',
     'DifferentialCommitMessageCustomField' => 'applications/differential/field/DifferentialCommitMessageCustomField.php',
     'DifferentialCommitMessageField' => 'applications/differential/field/DifferentialCommitMessageField.php',
     'DifferentialCommitMessageFieldTestCase' => 'applications/differential/field/__tests__/DifferentialCommitMessageFieldTestCase.php',
@@ -6588,6 +6589,7 @@
     'DifferentialChangesetTwoUpTestRenderer' => 'DifferentialChangesetTestRenderer',
     'DifferentialChangesetViewController' => 'DifferentialController',
     'DifferentialCloseConduitAPIMethod' => 'DifferentialConduitAPIMethod',
+    'DifferentialCoAuthorsCommitMessageField' => 'DifferentialCommitMessageField',
     'DifferentialCommitMessageCustomField' => 'DifferentialCommitMessageField',
     'DifferentialCommitMessageField' => 'Phobject',
     'DifferentialCommitMessageFieldTestCase' => 'PhabricatorTestCase',
diff --git a/src/applications/differential/conduit/DifferentialGetCommitMessageConduitAPIMethod.php b/src/applications/differential/conduit/DifferentialGetCommitMessageConduitAPIMethod.php
--- a/src/applications/differential/conduit/DifferentialGetCommitMessageConduitAPIMethod.php
+++ b/src/applications/differential/conduit/DifferentialGetCommitMessageConduitAPIMethod.php
@@ -95,6 +95,7 @@
     }
 
     $key_title = DifferentialTitleCommitMessageField::FIELDKEY;
+    $key_co_authors = DifferentialCoAuthorsCommitMessageField::FIELDKEY;
 
     $commit_message = array();
     foreach ($field_list as $field_key => $field) {
@@ -114,13 +115,14 @@
       }
 
       $is_title = ($field_key == $key_title);
+      $is_co_authors = ($field_key == $key_co_authors);
 
       if (!strlen($value)) {
         if ($is_template) {
           $commit_message[] = $label.': ';
         }
       } else {
-        if ($is_title) {
+        if ($is_title || $is_co_authors) {
           $commit_message[] = $value;
         } else {
           $value = str_replace(
diff --git a/src/applications/differential/field/DifferentialCoAuthorsCommitMessageField.php b/src/applications/differential/field/DifferentialCoAuthorsCommitMessageField.php
new file mode 100644
--- /dev/null
+++ b/src/applications/differential/field/DifferentialCoAuthorsCommitMessageField.php
@@ -0,0 +1,121 @@
+<?php
+
+final class DifferentialCoAuthorsCommitMessageField
+  extends DifferentialCommitMessageField {
+
+  const FIELDKEY = 'co-authors';
+
+  /**
+   * @var array<string, string|null>
+   */
+  protected $userEmailCache = array();
+
+  /**
+   * @var string
+   */
+  protected $authorPHID = null;
+
+  /**
+   * @var string[]
+   */
+  protected $coAuthors = array();
+
+  /**
+   * @return string
+   */
+  public function getFieldName() {
+    return pht('Co-Authors');
+  }
+
+  /**
+   * @return number
+   */
+  public function getFieldOrder() {
+    return 9999999;
+  }
+
+  /**
+   * @param  string $value
+   * @return bool
+   */
+  public function validateFieldValue($value) {
+    return true;
+  }
+
+  /**
+   * @return bool
+   */
+  public function isFieldEditable() {
+    return false;
+  }
+
+  /**
+   * @return bool
+   */
+  public function isTemplateField() {
+    return false;
+  }
+
+  /**
+   * @param  string $email
+   *
+   * @return string|null
+   */
+  protected function getUserPHID($email) {
+    if (!array_key_exists($email, $this->userEmailCache)) {
+      $this->userEmailCache[$email] = (new DiffusionResolveUserQuery())
+        ->withName($email)
+        ->execute();
+    }
+
+    return $this->userEmailCache[$email];
+  }
+
+  /**
+   * @param DifferentialRevision<mixed> $revision
+   *
+   * @return string
+   */
+  public function readFieldValueFromObject(DifferentialRevision $revision) {
+    $this->authorPHID = $revision->getAuthorPHID();
+    $diff_properties = $revision->getActiveDiff()
+      ->getDiffAuthorshipDict()['properties'];
+
+    if (!array_key_exists('local:commits', $diff_properties)) {
+      return '';
+    }
+
+    foreach ($diff_properties['local:commits'] as $commit) {
+      $this->addCoAuthor($commit['author'], $commit['authorEmail']);
+
+      if (array_key_exists('coAuthors', $commit)) {
+        foreach ($commit['coAuthors'] as $co_author) {
+          $this->addCoAuthor($co_author['name'], $co_author['email']);
+        }
+      }
+    }
+
+    return implode("\n", $this->getCoAuthors());
+  }
+
+  /**
+   * @param string $name
+   * @param string $email
+   *
+   * @return void
+   */
+  protected function addCoAuthor($name, $email) {
+    if ($this->getUserPHID($email) === $this->authorPHID) {
+      return;
+    }
+
+    $this->coAuthors[] = pht('Co-authored-by: %s <%s>', $name, $email);
+  }
+
+  /**
+   * @return string[]
+   */
+  protected function getCoAuthors() {
+    return array_unique($this->coAuthors);
+  }
+}
diff --git a/src/applications/diffusion/query/DiffusionResolveUserQuery.php b/src/applications/diffusion/query/DiffusionResolveUserQuery.php
--- a/src/applications/diffusion/query/DiffusionResolveUserQuery.php
+++ b/src/applications/diffusion/query/DiffusionResolveUserQuery.php
@@ -9,11 +9,19 @@
 
   private $name;
 
+  /**
+   * @param  string $name
+   *
+   * @return self
+   */
   public function withName($name) {
     $this->name = $name;
     return $this;
   }
 
+  /**
+   * @return string|null
+   */
   public function execute() {
     return $this->findUserPHID($this->name);
   }