diff --git a/lib/Events/BotInvokeEvent.php b/lib/Events/BotInvokeEvent.php
index 27146d680c1..b508a463720 100644
--- a/lib/Events/BotInvokeEvent.php
+++ b/lib/Events/BotInvokeEvent.php
@@ -11,20 +11,36 @@
 use OCP\EventDispatcher\Event;
 
 /**
+ * @psalm-type ChatMessageParentData = array{
+ *     type: 'Note',
+ *     actor: array{
+ *         type: 'Person',
+ *         id: non-empty-string,
+ *         name: non-empty-string,
+ *     },
+ *     object: array{
+ *         type: 'Note',
+ *         id: numeric-string,
+ *         name: string,
+ *         content: non-empty-string,
+ *         mediaType: 'text/markdown'|'text/plain',
+ *     },
+ * }
  * @psalm-type ChatMessageData = array{
  *     type: 'Activity'|'Create',
  *     actor: array{
  *         type: 'Person',
  *         id: non-empty-string,
  *         name: non-empty-string,
- *         talkParticipantType: non-empty-string,
+ *         talkParticipantType: numeric-string,
  *     },
  *     object: array{
  *         type: 'Note',
- *         id: non-empty-string,
+ *         id: numeric-string,
  *         name: string,
  *         content: non-empty-string,
  *         mediaType: 'text/markdown'|'text/plain',
+ *         inReplyTo?: ChatMessageParentData,
  *     },
  *     target: array{
  *         type: 'Collection',
diff --git a/lib/Service/ActivityPubHelper.php b/lib/Service/ActivityPubHelper.php
new file mode 100644
index 00000000000..8d649093483
--- /dev/null
+++ b/lib/Service/ActivityPubHelper.php
@@ -0,0 +1,87 @@
+<?php
+
+namespace OCA\Talk\Service;
+
+use OCA\Talk\Events\BotInvokeEvent;
+use OCA\Talk\Model\Attendee;
+use OCA\Talk\Model\BotServer;
+use OCA\Talk\Model\Message;
+use OCA\Talk\Room;
+use OCP\Comments\IComment;
+
+/**
+ * @psalm-import-type ChatMessageParentData from BotInvokeEvent
+ * @psalm-type NoteType = array{type: 'Note', id: numeric-string, name: string, content: string, mediaType: 'text/markdown'|'text/plain'}
+ */
+class ActivityPubHelper {
+	/**
+	 * @return array{type: 'Application', id: non-falsy-string, name: string}
+	 */
+	public function generateApplicationFromBot(BotServer $bot): array {
+		return [
+			'type' => 'Application',
+			'id' => Attendee::ACTOR_BOTS . '/' . Attendee::ACTOR_BOT_PREFIX . $bot->getUrlHash(),
+			'name' => $bot->getName(),
+		];
+	}
+
+	/**
+	 * @return array{type: 'Collection', id: non-empty-string, name: string}
+	 */
+	public function generateCollectionFromRoom(Room $room): array {
+		/** @var non-empty-string $token */
+		$token = $room->getToken();
+		return [
+			'type' => 'Collection',
+			'id' => $token,
+			'name' => $room->getName(),
+		];
+	}
+
+	/**
+	 * @psalm-param ?ChatMessageParentData $inReplyTo
+	 * @psalm-return NoteType&array{inReplyTo?: ChatMessageParentData}
+	 */
+	public function generateNote(IComment $comment, array $messageData, string $messageType, ?array $inReplyTo = null): array {
+		/** @var string $content */
+		$content = json_encode($messageData, JSON_THROW_ON_ERROR);
+		/** @var numeric-string $messageId */
+		$messageId = $comment->getId();
+		/** @var 'text/markdown'|'text/plain' $mediaType */
+		$mediaType = 'text/markdown';// FIXME or text/plain when markdown is disabled
+		$note = [
+			'type' => 'Note',
+			'id' => $messageId,
+			'name' => $messageType,
+			'content' => $content,
+			'mediaType' => $mediaType,
+		];
+		if ($inReplyTo !== null) {
+			$note['inReplyTo'] = $inReplyTo;
+		}
+		return $note;
+	}
+
+	/**
+	 * @return array{type: 'Person', id: non-falsy-string, name: string, talkParticipantType: numeric-string}
+	 */
+	public function generatePersonFromAttendee(Attendee $attendee): array {
+		return [
+			'type' => 'Person',
+			'id' => $attendee->getActorType() . '/' . $attendee->getActorId(),
+			'name' => $attendee->getDisplayName(),
+			'talkParticipantType' => (string)$attendee->getParticipantType(),
+		];
+	}
+
+	/**
+	 * @return array{type: 'Person', id: non-falsy-string, name: string}
+	 */
+	public function generatePersonFromMessageActor(Message $message): array {
+		return [
+			'type' => 'Person',
+			'id' => $message->getActorType() . '/' . $message->getActorId(),
+			'name' => $message->getActorDisplayName(),
+		];
+	}
+}
diff --git a/lib/Service/BotService.php b/lib/Service/BotService.php
index ba3f0e85684..dacee94f0af 100644
--- a/lib/Service/BotService.php
+++ b/lib/Service/BotService.php
@@ -46,6 +46,8 @@
  * @psalm-import-type InvocationData from BotInvokeEvent
  */
 class BotService {
+	private ActivityPubHelper $activityPubHelper;
+
 	public function __construct(
 		protected BotServerMapper $botServerMapper,
 		protected BotConversationMapper $botConversationMapper,
@@ -62,37 +64,22 @@ public function __construct(
 		protected ICertificateManager $certificateManager,
 		protected IEventDispatcher $dispatcher,
 	) {
+		$this->activityPubHelper = new ActivityPubHelper();
 	}
 
 	public function afterBotEnabled(BotEnabledEvent $event): void {
 		$this->invokeBots([$event->getBotServer()], $event->getRoom(), null, [
 			'type' => 'Join',
-			'actor' => [
-				'type' => 'Application',
-				'id' => Attendee::ACTOR_BOTS . '/' . Attendee::ACTOR_BOT_PREFIX . $event->getBotServer()->getUrlHash(),
-				'name' => $event->getBotServer()->getName(),
-			],
-			'object' => [
-				'type' => 'Collection',
-				'id' => $event->getRoom()->getToken(),
-				'name' => $event->getRoom()->getName(),
-			],
+			'actor' => $this->activityPubHelper->generateApplicationFromBot($event->getBotServer()),
+			'object' => $this->activityPubHelper->generateCollectionFromRoom($event->getRoom()),
 		]);
 	}
 
 	public function afterBotDisabled(BotDisabledEvent $event): void {
 		$this->invokeBots([$event->getBotServer()], $event->getRoom(), null, [
 			'type' => 'Leave',
-			'actor' => [
-				'type' => 'Application',
-				'id' => Attendee::ACTOR_BOTS . '/' . Attendee::ACTOR_BOT_PREFIX . $event->getBotServer()->getUrlHash(),
-				'name' => $event->getBotServer()->getName(),
-			],
-			'object' => [
-				'type' => 'Collection',
-				'id' => $event->getRoom()->getToken(),
-				'name' => $event->getRoom()->getName(),
-			],
+			'actor' => $this->activityPubHelper->generateApplicationFromBot($event->getBotServer()),
+			'object' => $this->activityPubHelper->generateCollectionFromRoom($event->getRoom()),
 		]);
 	}
 
@@ -108,6 +95,28 @@ public function afterChatMessageSent(ChatMessageSentEvent $event, MessageParser
 			return;
 		}
 
+		$inReplyTo = null;
+		$parent = $event->getParent();
+		if ($parent instanceof IComment) {
+			$parentMessage = $messageParser->createMessage(
+				$event->getRoom(),
+				$event->getParticipant(),
+				$parent,
+				$this->l10nFactory->get('spreed', 'en', 'en')
+			);
+			$messageParser->parseMessage($parentMessage);
+			$parentMessageData = [
+				'message' => $parentMessage->getMessage(),
+				'parameters' => $parentMessage->getMessageParameters(),
+			];
+
+			$inReplyTo = [
+				'type' => 'Note',
+				'actor' => $this->activityPubHelper->generatePersonFromMessageActor($parentMessage),
+				'object' => $this->activityPubHelper->generateNote($parent, $parentMessageData, 'message'),
+			];
+		}
+
 		$message = $messageParser->createMessage(
 			$event->getRoom(),
 			$event->getParticipant(),
@@ -124,24 +133,9 @@ public function afterChatMessageSent(ChatMessageSentEvent $event, MessageParser
 
 		$this->invokeBots($botServers, $event->getRoom(), $event->getComment(), [
 			'type' => 'Create',
-			'actor' => [
-				'type' => 'Person',
-				'id' => $attendee->getActorType() . '/' . $attendee->getActorId(),
-				'name' => $attendee->getDisplayName(),
-				'talkParticipantType' => (string)$attendee->getParticipantType(),
-			],
-			'object' => [
-				'type' => 'Note',
-				'id' => $event->getComment()->getId(),
-				'name' => 'message',
-				'content' => json_encode($messageData, JSON_THROW_ON_ERROR),
-				'mediaType' => 'text/markdown', // FIXME or text/plain when markdown is disabled
-			],
-			'target' => [
-				'type' => 'Collection',
-				'id' => $event->getRoom()->getToken(),
-				'name' => $event->getRoom()->getName(),
-			]
+			'actor' => $this->activityPubHelper->generatePersonFromAttendee($attendee),
+			'object' => $this->activityPubHelper->generateNote($event->getComment(), $messageData, 'message', $inReplyTo),
+			'target' => $this->activityPubHelper->generateCollectionFromRoom($event->getRoom()),
 		]);
 	}
 
@@ -167,23 +161,9 @@ public function afterSystemMessageSent(SystemMessageSentEvent $event, MessagePar
 
 		$this->invokeBots($botServers, $event->getRoom(), $event->getComment(), [
 			'type' => 'Activity',
-			'actor' => [
-				'type' => 'Person',
-				'id' => $message->getActorType() . '/' . $message->getActorId(),
-				'name' => $message->getActorDisplayName(),
-			],
-			'object' => [
-				'type' => 'Note',
-				'id' => $event->getComment()->getId(),
-				'name' => $message->getMessageRaw(),
-				'content' => json_encode($messageData),
-				'mediaType' => 'text/markdown',
-			],
-			'target' => [
-				'type' => 'Collection',
-				'id' => $event->getRoom()->getToken(),
-				'name' => $event->getRoom()->getName(),
-			]
+			'actor' => $this->activityPubHelper->generatePersonFromMessageActor($message),
+			'object' => $this->activityPubHelper->generateNote($event->getComment(), $messageData, $message->getMessageRaw()),
+			'target' => $this->activityPubHelper->generateCollectionFromRoom($event->getRoom()),
 		]);
 	}