diff --git a/homeassistant/components/google_generative_ai_conversation/conversation.py b/homeassistant/components/google_generative_ai_conversation/conversation.py
index 5460f48f20e..7c19c5445a7 100644
--- a/homeassistant/components/google_generative_ai_conversation/conversation.py
+++ b/homeassistant/components/google_generative_ai_conversation/conversation.py
@@ -356,6 +356,15 @@ class GoogleGenerativeAIConversationEntity(
 
             messages.append(_convert_content(chat_content))
 
+        # The SDK requires the first message to be a user message
+        # This is not the case if user used `start_conversation`
+        # Workaround from https://github.com/googleapis/python-genai/issues/529#issuecomment-2740964537
+        if messages and messages[0].role != "user":
+            messages.insert(
+                0,
+                Content(role="user", parts=[Part.from_text(text=" ")]),
+            )
+
         if tool_results:
             messages.append(_create_google_tool_response_content(tool_results))
         generateContentConfig = GenerateContentConfig(
diff --git a/tests/components/google_generative_ai_conversation/test_conversation.py b/tests/components/google_generative_ai_conversation/test_conversation.py
index a2b238b9399..9c4ecc4f9a4 100644
--- a/tests/components/google_generative_ai_conversation/test_conversation.py
+++ b/tests/components/google_generative_ai_conversation/test_conversation.py
@@ -715,3 +715,48 @@ async def test_empty_content_in_chat_history(
 
         assert actual_history[0].parts[0].text == first_input
         assert actual_history[1].parts[0].text == " "
+
+
+@pytest.mark.usefixtures("mock_init_component")
+async def test_history_always_user_first_turn(
+    hass: HomeAssistant,
+    mock_config_entry: MockConfigEntry,
+    snapshot: SnapshotAssertion,
+) -> None:
+    """Test that the user is always first in the chat history."""
+    with (
+        chat_session.async_get_chat_session(hass) as session,
+        async_get_chat_log(hass, session) as chat_log,
+    ):
+        chat_log.async_add_assistant_content_without_tools(
+            conversation.AssistantContent(
+                agent_id="conversation.google_generative_ai_conversation",
+                content="Garage door left open, do you want to close it?",
+            )
+        )
+
+    with patch("google.genai.chats.AsyncChats.create") as mock_create:
+        mock_chat = AsyncMock()
+        mock_create.return_value.send_message = mock_chat
+        chat_response = Mock(prompt_feedback=None)
+        mock_chat.return_value = chat_response
+        chat_response.candidates = [Mock(content=Mock(parts=[]))]
+
+        await conversation.async_converse(
+            hass,
+            "hello",
+            chat_log.conversation_id,
+            Context(),
+            agent_id="conversation.google_generative_ai_conversation",
+        )
+
+    _, kwargs = mock_create.call_args
+    actual_history = kwargs.get("history")
+
+    assert actual_history[0].parts[0].text == " "
+    assert actual_history[0].role == "user"
+    assert (
+        actual_history[1].parts[0].text
+        == "Garage door left open, do you want to close it?"
+    )
+    assert actual_history[1].role == "model"