diff --git a/artifacts/api-server/src/routes/conversations.ts b/artifacts/api-server/src/routes/conversations.ts
index f9113216..5a41ac6a 100644
--- a/artifacts/api-server/src/routes/conversations.ts
+++ b/artifacts/api-server/src/routes/conversations.ts
@@ -1,5 +1,5 @@
 import { Router, type IRouter } from "express";
-import { eq, and, desc, sql } from "drizzle-orm";
+import { eq, and, desc, asc, sql } from "drizzle-orm";
 import { db } from "@workspace/db";
 import {
   conversationsTable,
@@ -645,11 +645,68 @@ router.post(
       return;
     }
 
-    if (!(await isConversationMember(params.data.id, userId))) {
+    const participants = await db
+      .select({
+        userId: conversationParticipantsTable.userId,
+        isAdmin: conversationParticipantsTable.isAdmin,
+        joinedAt: conversationParticipantsTable.joinedAt,
+      })
+      .from(conversationParticipantsTable)
+      .where(eq(conversationParticipantsTable.conversationId, params.data.id))
+      .orderBy(asc(conversationParticipantsTable.joinedAt));
+
+    const leaver = participants.find((p) => p.userId === userId);
+    if (!leaver) {
       res.status(403).json({ error: "Forbidden" });
       return;
     }
 
+    const remaining = participants.filter((p) => p.userId !== userId);
+
+    // If leaver was the only participant, clean up the conversation entirely.
+    if (remaining.length === 0) {
+      await db
+        .delete(conversationsTable)
+        .where(eq(conversationsTable.id, params.data.id));
+      await evictUserFromConversationRoom(userId, params.data.id);
+      res.json({ success: true });
+      return;
+    }
+
+    // Determine if we need to promote a successor admin.
+    const leaverWasOnlyAdmin =
+      leaver.isAdmin && !remaining.some((p) => p.isAdmin);
+    const successor = leaverWasOnlyAdmin ? remaining[0] : null;
+
+    if (successor) {
+      await db
+        .update(conversationParticipantsTable)
+        .set({ isAdmin: true })
+        .where(
+          and(
+            eq(conversationParticipantsTable.conversationId, params.data.id),
+            eq(conversationParticipantsTable.userId, successor.userId),
+          ),
+        );
+    }
+
+    // Announce the leave (and promotion) before removing the leaver so the
+    // system message has a sensible actor and members see it in real time.
+    const actor = await getUserDisplay(userId);
+    await insertAndEmitSystemMessage(params.data.id, userId, "member_left", {
+      actor,
+    });
+
+    if (successor) {
+      const promoted = await getUserDisplay(successor.userId);
+      await insertAndEmitSystemMessage(
+        params.data.id,
+        successor.userId,
+        "admin_promoted",
+        { promoted, reason: "previous_admin_left" },
+      );
+    }
+
     await db
       .delete(conversationParticipantsTable)
       .where(
diff --git a/artifacts/teaboy-os/src/locales/ar.json b/artifacts/teaboy-os/src/locales/ar.json
index d2cfd102..90a990c0 100644
--- a/artifacts/teaboy-os/src/locales/ar.json
+++ b/artifacts/teaboy-os/src/locales/ar.json
@@ -188,7 +188,10 @@
       "groupRenamed": "غيّر {{actor}} اسم المجموعة إلى \"{{name}}\"",
       "membersAdded_one": "أضاف {{actor}} {{names}}",
       "membersAdded_other": "أضاف {{actor}} {{names}}",
-      "memberRemoved": "أزال {{actor}} {{target}}"
+      "memberRemoved": "أزال {{actor}} {{target}}",
+      "memberLeft": "غادر {{actor}} المجموعة",
+      "adminPromoted": "{{target}} أصبح مشرفًا للمجموعة",
+      "adminPromotedAfterLeave": "تمت ترقية {{target}} إلى مشرف بعد مغادرة المشرف السابق"
     }
   },
   "notifications": {
diff --git a/artifacts/teaboy-os/src/locales/en.json b/artifacts/teaboy-os/src/locales/en.json
index 9242c53b..fbb87519 100644
--- a/artifacts/teaboy-os/src/locales/en.json
+++ b/artifacts/teaboy-os/src/locales/en.json
@@ -185,7 +185,10 @@
       "groupRenamed": "{{actor}} renamed the group to \"{{name}}\"",
       "membersAdded_one": "{{actor}} added {{names}}",
       "membersAdded_other": "{{actor}} added {{names}}",
-      "memberRemoved": "{{actor}} removed {{target}}"
+      "memberRemoved": "{{actor}} removed {{target}}",
+      "memberLeft": "{{actor}} left the group",
+      "adminPromoted": "{{target}} is now a group admin",
+      "adminPromotedAfterLeave": "{{target}} was promoted to admin after the previous admin left"
     }
   },
   "notifications": {
diff --git a/artifacts/teaboy-os/src/pages/chat.tsx b/artifacts/teaboy-os/src/pages/chat.tsx
index d94607b7..f8bbbcda 100644
--- a/artifacts/teaboy-os/src/pages/chat.tsx
+++ b/artifacts/teaboy-os/src/pages/chat.tsx
@@ -70,6 +70,8 @@ type SystemMessageMeta = {
   newNameEn?: string | null;
   addedUsers?: UserDisplay[];
   removedUser?: UserDisplay | null;
+  promoted?: UserDisplay | null;
+  reason?: string | null;
 };
 
 type SystemRenderable = {
@@ -106,6 +108,17 @@ function renderSystemMessage(
       const target = pickDisplayName(meta.removedUser, lang) || t("chat.system.someone");
       return t("chat.system.memberRemoved", { actor, target });
     }
+    case "member_left": {
+      return t("chat.system.memberLeft", { actor });
+    }
+    case "admin_promoted": {
+      const target = pickDisplayName(meta.promoted, lang) || t("chat.system.someone");
+      const key =
+        meta.reason === "previous_admin_left"
+          ? "chat.system.adminPromotedAfterLeave"
+          : "chat.system.adminPromoted";
+      return t(key, { target });
+    }
     default:
       return "";
   }