diff --git a/bec_widgets/qt_utils/toolbar.py b/bec_widgets/qt_utils/toolbar.py
index da17b221..3ae2f45b 100644
--- a/bec_widgets/qt_utils/toolbar.py
+++ b/bec_widgets/qt_utils/toolbar.py
@@ -486,6 +486,52 @@ class ModularToolBar(QToolBar):
 
         self.update_separators()  # Update separators after adding the bundle
 
+    def add_action_to_bundle(self, bundle_id: str, action_id: str, action, target_widget: QWidget):
+        """
+        Dynamically adds a new action to an existing toolbar bundle.
+
+        Args:
+            bundle_id (str): The ID of the bundle to extend.
+            action_id (str): Unique identifier for the new action.
+            action (ToolBarAction): The action instance to add.
+            target_widget (QWidget): The target widget for the action.
+        """
+        if bundle_id not in self.bundles:
+            raise ValueError(f"Bundle '{bundle_id}' does not exist.")
+        if action_id in self.widgets:
+            raise ValueError(f"Action with ID '{action_id}' already exists.")
+
+        # Add the new action temporarily to create its QAction
+        action.add_to_toolbar(self, target_widget)
+        new_qaction = action.action
+
+        # Remove the newly added action from its default position
+        self.removeAction(new_qaction)
+
+        # Find the last action in the existing bundle to determine insertion point
+        bundle_action_ids = self.bundles[bundle_id]
+        if bundle_action_ids:
+            last_bundle_action = self.widgets[bundle_action_ids[-1]].action
+            actions_list = self.actions()
+            try:
+                index = actions_list.index(last_bundle_action)
+            except ValueError:
+                self.addAction(new_qaction)
+            else:
+                if index + 1 < len(actions_list):
+                    before_action = actions_list[index + 1]
+                    self.insertAction(before_action, new_qaction)
+                else:
+                    self.addAction(new_qaction)
+        else:
+            # If bundle is empty, simply add the action at the end
+            self.addAction(new_qaction)
+
+        # Update internal tracking
+        self.widgets[action_id] = action
+        self.bundles[bundle_id].append(action_id)
+        self.update_separators()
+
     def contextMenuEvent(self, event):
         """
         Overrides the context menu event to show a list of toolbar actions with checkboxes and icons, including separators.
@@ -664,6 +710,13 @@ class MainWindow(QMainWindow):  # pragma: no cover
         )
         self.toolbar.add_bundle(second_bundle, target_widget=self)
 
+        new_action = MaterialIconAction(
+            icon_name="counter_1", tooltip="New Action", checkable=True, parent=self
+        )
+        self.toolbar.add_action_to_bundle(
+            "main_actions", "new_action", new_action, target_widget=self
+        )
+
 
 if __name__ == "__main__":  # pragma: no cover
     app = QApplication(sys.argv)
diff --git a/tests/unit_tests/test_modular_toolbar.py b/tests/unit_tests/test_modular_toolbar.py
index c54baade..17440232 100644
--- a/tests/unit_tests/test_modular_toolbar.py
+++ b/tests/unit_tests/test_modular_toolbar.py
@@ -318,6 +318,38 @@ def test_widget_action_calculate_minimum_width(qtbot):
     assert width > 100
 
 
+def test_add_action_to_bundle(toolbar_fixture, dummy_widget, material_icon_action):
+    # Create an initial bundle with one action
+    bundle = ToolbarBundle(
+        bundle_id="test_bundle", actions=[("initial_action", material_icon_action)]
+    )
+    toolbar_fixture.add_bundle(bundle, dummy_widget)
+
+    # Create a new action to add to the existing bundle
+    new_action = MaterialIconAction(
+        icon_name="counter_1", tooltip="New Action", checkable=True, parent=dummy_widget
+    )
+    toolbar_fixture.add_action_to_bundle("test_bundle", "new_action", new_action, dummy_widget)
+
+    # Verify the new action is registered in the toolbar's widgets
+    assert "new_action" in toolbar_fixture.widgets
+    assert toolbar_fixture.widgets["new_action"] == new_action
+
+    # Verify the new action is included in the bundle tracking
+    assert "new_action" in toolbar_fixture.bundles["test_bundle"]
+    assert toolbar_fixture.bundles["test_bundle"][-1] == "new_action"
+
+    # Verify the new action's QAction is present in the toolbar's action list
+    actions_list = toolbar_fixture.actions()
+    assert new_action.action in actions_list
+
+    # Verify that the new action is inserted immediately after the last action of the bundle
+    last_bundle_action = material_icon_action.action
+    index_last = actions_list.index(last_bundle_action)
+    index_new = actions_list.index(new_action.action)
+    assert index_new == index_last + 1
+
+
 # FIXME test is stucking CI, works locally
 # def test_context_menu_contains_added_actions(
 #     qtbot, icon_action, material_icon_action, dummy_widget