diff --git a/components/ai_chat/core/common/BUILD.gn b/components/ai_chat/core/common/BUILD.gn
index e1080ea7705a..1a3d36a5cb29 100644
--- a/components/ai_chat/core/common/BUILD.gn
+++ b/components/ai_chat/core/common/BUILD.gn
@@ -21,3 +21,18 @@ static_library("common") {
     "//components/prefs",
   ]
 }
+
+if (!is_ios) {
+  source_set("unit_tests") {
+    testonly = true
+    sources = [ "pref_names_unittest.cc" ]
+
+    deps = [
+      "//base/test:test_support",
+      "//brave/components/ai_chat/core/common",
+      "//components/prefs:test_support",
+      "//content/test:test_support",
+      "//testing/gtest:gtest",
+    ]
+  }
+}
diff --git a/components/ai_chat/core/common/pref_names.cc b/components/ai_chat/core/common/pref_names.cc
index a60a8e0e2d44..6e144200ad2b 100644
--- a/components/ai_chat/core/common/pref_names.cc
+++ b/components/ai_chat/core/common/pref_names.cc
@@ -5,6 +5,9 @@
 
 #include "brave/components/ai_chat/core/common/pref_names.h"
 
+#include <string>
+
+#include "base/strings/string_util.h"
 #include "brave/components/ai_chat/core/common/features.h"
 #include "components/prefs/pref_registry_simple.h"
 #include "components/prefs/pref_service.h"
@@ -38,7 +41,16 @@ void RegisterProfilePrefsForMigration(PrefRegistrySimple* registry) {
 
 void MigrateProfilePrefs(PrefService* profile_prefs) {
   profile_prefs->ClearPref(kObseleteBraveChatAutoGenerateQuestions);
-  // TODO(petemill): migrate model key from "chat-default" to "chat-basic"
+  // migrate model key from "chat-default" to "chat-basic"
+  static const std::string kDefaultModelBasicFrom = "chat-default";
+  static const std::string kDefaultModelBasicTo = "chat-basic";
+  if (auto* default_model_value =
+          profile_prefs->GetUserPrefValue(kDefaultModelKey)) {
+    if (base::EqualsCaseInsensitiveASCII(default_model_value->GetString(),
+                                         kDefaultModelBasicFrom)) {
+      profile_prefs->SetString(kDefaultModelKey, kDefaultModelBasicTo);
+    }
+  }
 }
 
 void RegisterLocalStatePrefs(PrefRegistrySimple* registry) {
diff --git a/components/ai_chat/core/common/pref_names_unittest.cc b/components/ai_chat/core/common/pref_names_unittest.cc
new file mode 100644
index 000000000000..bcdcc236210e
--- /dev/null
+++ b/components/ai_chat/core/common/pref_names_unittest.cc
@@ -0,0 +1,33 @@
+// Copyright (c) 2024 The Brave Authors. All rights reserved.
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this file,
+// You can obtain one at https://mozilla.org/MPL/2.0/.
+
+#include "brave/components/ai_chat/core/common/pref_names.h"
+
+#include <string>
+
+#include "components/prefs/testing_pref_service.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+namespace ai_chat::prefs {
+
+class AIChatPrefMigrationTest : public ::testing::Test {
+ public:
+  void SetUp() override {
+    RegisterProfilePrefs(pref_service_.registry());
+    RegisterProfilePrefsForMigration(pref_service_.registry());
+  }
+
+  TestingPrefServiceSimple pref_service_;
+};
+
+TEST_F(AIChatPrefMigrationTest, ChangeOldDefaultKey) {
+  pref_service_.SetString(kDefaultModelKey, "chat-default");
+  MigrateProfilePrefs(&pref_service_);
+
+  EXPECT_EQ(pref_service_.GetUserPrefValue(kDefaultModelKey)->GetString(),
+            "chat-basic");
+}
+
+}  // namespace ai_chat::prefs
diff --git a/test/BUILD.gn b/test/BUILD.gn
index 59489cd991ba..db4124db5d9f 100644
--- a/test/BUILD.gn
+++ b/test/BUILD.gn
@@ -361,6 +361,7 @@ test("brave_unit_tests") {
     deps += [
       "//brave/browser/ai_chat:unit_tests",
       "//brave/components/ai_chat/core/browser:unit_tests",
+      "//brave/components/ai_chat/core/common:unit_tests",
     ]
   }