diff --git a/esphome/components/api/__init__.py b/esphome/components/api/__init__.py
index 0f5cd936f5..1146b43596 100644
--- a/esphome/components/api/__init__.py
+++ b/esphome/components/api/__init__.py
@@ -540,17 +540,20 @@ HOMEASSISTANT_ACTION_ACTION_SCHEMA = cv.All(
 )
 
 
+# synchronous=False: when on_success/on_error is configured, play() stores the
+# trigger args until the HomeassistantActionResponse arrives, so non-owning args
+# (StringRef into the API receive buffer) must not be used.
 @automation.register_action(
     "homeassistant.action",
     HomeAssistantServiceCallAction,
     HOMEASSISTANT_ACTION_ACTION_SCHEMA,
-    synchronous=True,
+    synchronous=False,
 )
 @automation.register_action(
     "homeassistant.service",
     HomeAssistantServiceCallAction,
     HOMEASSISTANT_ACTION_ACTION_SCHEMA,
-    synchronous=True,
+    synchronous=False,
 )
 async def homeassistant_service_to_code(
     config: ConfigType,
@@ -644,6 +647,8 @@ HOMEASSISTANT_EVENT_ACTION_SCHEMA = cv.Schema(
 )
 
 
+# synchronous=True is safe here: the event schema has no on_success/on_error,
+# so play() never stores the trigger args.
 @automation.register_action(
     "homeassistant.event",
     HomeAssistantServiceCallAction,
diff --git a/tests/component_tests/api/__init__.py b/tests/component_tests/api/__init__.py
new file mode 100644
index 0000000000..e69de29bb2
diff --git a/tests/component_tests/api/test_homeassistant_action.py b/tests/component_tests/api/test_homeassistant_action.py
new file mode 100644
index 0000000000..611353e7c5
--- /dev/null
+++ b/tests/component_tests/api/test_homeassistant_action.py
@@ -0,0 +1,28 @@
+"""Tests for arg-type selection of api user-defined services with homeassistant.action."""
+
+CONFIG = "tests/component_tests/api/test_homeassistant_action.yaml"
+
+
+def test_synchronous_chain_keeps_zero_copy_args(generate_main):
+    """A chain of synchronous actions keeps the non-owning StringRef arg type."""
+    main_cpp = generate_main(CONFIG)
+
+    assert (
+        "api::UserServiceTrigger<api::enums::SUPPORTS_RESPONSE_NONE, StringRef>"
+        '("zero_copy_args", {"message"})' in main_cpp
+    )
+
+
+def test_response_callback_args_are_owning(generate_main):
+    """homeassistant.action with on_success/on_error stores the trigger args
+    until the HomeassistantActionResponse arrives, so string args must fall
+    back to owning std::string; StringRef would point into the connection's
+    receive buffer, which is reused before the response arrives."""
+    main_cpp = generate_main(CONFIG)
+
+    assert (
+        "api::UserServiceTrigger<api::enums::SUPPORTS_RESPONSE_NONE, std::string>"
+        '("response_args", {"message"})' in main_cpp
+    )
+    assert "api::HomeAssistantServiceCallAction<std::string>" in main_cpp
+    assert "api::HomeAssistantServiceCallAction<StringRef>" not in main_cpp
diff --git a/tests/component_tests/api/test_homeassistant_action.yaml b/tests/component_tests/api/test_homeassistant_action.yaml
new file mode 100644
index 0000000000..4561494c9e
--- /dev/null
+++ b/tests/component_tests/api/test_homeassistant_action.yaml
@@ -0,0 +1,43 @@
+esphome:
+  name: test
+
+esp32:
+  board: esp32dev
+
+wifi:
+  ssid: SomeNetwork
+  password: SomePassword
+
+logger:
+
+api:
+  actions:
+    # Chain of synchronous actions that never store the args:
+    # keeps the zero-copy StringRef arg type.
+    - action: zero_copy_args
+      variables:
+        message: string
+      then:
+        - logger.log:
+            format: "%s"
+            args: [message.c_str()]
+    # homeassistant.action with on_success/on_error stores the trigger args
+    # until the action response arrives, so the codegen must fall back to
+    # owning std::string args (StringRef would dangle once the receive
+    # buffer is reused).
+    - action: response_args
+      variables:
+        message: string
+      then:
+        - homeassistant.action:
+            action: notify.notify
+            data:
+              message: !lambda return message;
+            on_success:
+              - logger.log:
+                  format: "sent %s"
+                  args: [message.c_str()]
+            on_error:
+              - logger.log:
+                  format: "failed (%s): %s"
+                  args: [error.c_str(), message.c_str()]
diff --git a/tests/components/api/common-base.yaml b/tests/components/api/common-base.yaml
index 060254990d..d7470ee4b3 100644
--- a/tests/components/api/common-base.yaml
+++ b/tests/components/api/common-base.yaml
@@ -109,6 +109,34 @@ api:
               - name.c_str()
               - int_arr.size()
               - string_arr.size()
+    # Test string + array args used by homeassistant.action's deferred
+    # on_success/on_error response callback.  homeassistant.action registers
+    # synchronous=False, so the api codegen must fall back to owning
+    # std::string / std::vector args here: the non-owning defaults would
+    # dangle once rx_buf_ is reused before the response arrives, and the
+    # non-copyable FixedVector would fail to compile when captured into
+    # the response callback.
+    - action: action_response_args
+      variables:
+        name: string
+        int_arr: int[]
+      then:
+        - homeassistant.action:
+            action: notify.notify
+            data:
+              message: !lambda 'return name;'
+            on_success:
+              - logger.log:
+                  format: "Notified %s (%u ints)"
+                  args:
+                    - name.c_str()
+                    - int_arr.size()
+            on_error:
+              - logger.log:
+                  format: "Notify failed (%s): %s"
+                  args:
+                    - error.c_str()
+                    - name.c_str()
     # Test ContinuationAction (IfAction with then/else branches)
     - action: test_if_action
       variables: