diff --git a/.changeset/green-groups-identify.md b/.changeset/green-groups-identify.md
new file mode 100644
index 0000000..545a238
--- /dev/null
+++ b/.changeset/green-groups-identify.md
@@ -0,0 +1,5 @@
+---
+"posthog-php": minor
+---
+
+Add an optional `distinctId`/`distinct_id` override for `groupIdentify()` events.
diff --git a/bin/posthog b/bin/posthog
index 2568b50..49d8d40 100755
--- a/bin/posthog
+++ b/bin/posthog
@@ -81,13 +81,15 @@ switch ($options['type']) {
         break;
 
     case 'groupIdentify':
-        PostHog::groupIdentify(
-            array(
-                'groupType' => $options['groupType'],
-                'groupKey' => $options['groupKey'],
-                'properties' => parse_json($options['properties'])
-            )
+        $message = array(
+            'groupType' => $options['groupType'],
+            'groupKey' => $options['groupKey'],
+            'properties' => parse_json($options['properties'])
         );
+        if (!empty($options['distinctId'])) {
+            $message['distinctId'] = $options['distinctId'];
+        }
+        PostHog::groupIdentify($message);
         break;
 
     case 'getFeatureFlag':
@@ -121,7 +123,7 @@ function usage(): string
         "\n    posthog --type capture --distinctId \"id\" --event \"event name\" --properties '{ \"json\": \"object\" }'" .
         "\n    posthog --type identify --distinctId \"id\" --properties '{ \"json\": \"object\" }'" .
         "\n    posthog --type alias --distinctId \"id\" --alias \"alias\"" .
-        "\n    posthog --type groupIdentify --groupType \"organization\" --groupKey \"id:5\" --properties '{ \"json\": \"object\" }'" .
+        "\n    posthog --type groupIdentify --groupType \"organization\" --groupKey \"id:5\" --distinctId \"user-id\" --properties '{ \"json\": \"object\" }'" .
         "\n    posthog --type getFeatureFlag --flag some-flag --apiKey phc_... --host localhost:8010 --no-ssl" .
         "\n    posthog --type getFeatureFlag --flag some-flag --apiKey phc_... --host localhost:8010 --no-ssl" .
         "\n\n\n";
diff --git a/lib/PostHog.php b/lib/PostHog.php
index 6dbe3fc..c4b76bf 100644
--- a/lib/PostHog.php
+++ b/lib/PostHog.php
@@ -110,7 +110,8 @@ public static function identify(array $message)
     /**
      * Adds properties to a group.
      *
-     * @param array $message Must contain keys `groupType`, `groupKey`, `properties`
+     * @param array $message Must contain keys `groupType`, `groupKey`; accepts optional `properties`
+     *                       and `distinctId`/`distinct_id` to override the default synthetic ID.
      * @return boolean whether the groupIdentify call succeeded
      * @throws Exception
      */
@@ -123,9 +124,24 @@ public static function groupIdentify(array $message)
             $message["properties"] = array();
         }
 
+        $distinctId = "\${$message['groupType']}_{$message['groupKey']}";
+        if (
+            array_key_exists("distinctId", $message)
+            && is_scalar($message["distinctId"])
+            && (string) $message["distinctId"] !== ""
+        ) {
+            $distinctId = (string) $message["distinctId"];
+        } elseif (
+            array_key_exists("distinct_id", $message)
+            && is_scalar($message["distinct_id"])
+            && (string) $message["distinct_id"] !== ""
+        ) {
+            $distinctId = (string) $message["distinct_id"];
+        }
+
         $msg = array(
             "event" => "\$groupidentify",
-            "distinctId" => "\${$message['groupType']}_{$message['groupKey']}",
+            "distinctId" => $distinctId,
             "properties" => array(
                 "\$group_type" => $message["groupType"],
                 "\$group_key" => $message["groupKey"],
diff --git a/test/RequestContextTest.php b/test/RequestContextTest.php
index 5b21af6..7b025f3 100644
--- a/test/RequestContextTest.php
+++ b/test/RequestContextTest.php
@@ -438,6 +438,38 @@ public function testContextDoesNotMutateGroupIdentifyProperties(): void
         $this->assertArrayNotHasKey('$session_id', $event['properties']);
     }
 
+    public function testGroupIdentifyAllowsDistinctIdOverride(): void
+    {
+        PostHog::groupIdentify([
+            'groupType' => 'organization',
+            'groupKey' => 'acme',
+            'distinctId' => 'user-123',
+            'properties' => ['name' => 'Acme Inc.'],
+        ]);
+
+        $event = $this->flushAndGetEvents()[0];
+
+        $this->assertSame('user-123', $event['distinct_id']);
+        $this->assertSame('$groupidentify', $event['event']);
+        $this->assertSame('organization', $event['properties']['$group_type']);
+        $this->assertSame('acme', $event['properties']['$group_key']);
+        $this->assertSame(['name' => 'Acme Inc.'], $event['properties']['$group_set']);
+    }
+
+    public function testGroupIdentifyAllowsSnakeCaseDistinctIdOverride(): void
+    {
+        PostHog::groupIdentify([
+            'groupType' => 'organization',
+            'groupKey' => 'acme',
+            'distinct_id' => 'snake-user-123',
+            'properties' => ['name' => 'Acme Inc.'],
+        ]);
+
+        $event = $this->flushAndGetEvents()[0];
+
+        $this->assertSame('snake-user-123', $event['distinct_id']);
+    }
+
     public function testEvaluateFlagsUsesContextDistinctIdWhenOmitted(): void
     {
         PostHog::withContext(['distinctId' => 'context-user'], function (): void {