diff --git a/homeassistant/core.py b/homeassistant/core.py
index 528ab3f6d01..661f087fe6a 100644
--- a/homeassistant/core.py
+++ b/homeassistant/core.py
@@ -1768,7 +1768,7 @@ class ServiceRegistry:
         the context. Will return NONE if the service does not exist as there is
         other error handling when calling the service if it does not exist.
         """
-        if not (handler := self._services[domain][service]):
+        if not (handler := self._services[domain.lower()][service.lower()]):
             return SupportsResponse.NONE
         return handler.supports_response
 
diff --git a/homeassistant/helpers/service.py b/homeassistant/helpers/service.py
index 1164c2d8015..dcd7115f363 100644
--- a/homeassistant/helpers/service.py
+++ b/homeassistant/helpers/service.py
@@ -670,6 +670,9 @@ def async_set_service_schema(
     hass: HomeAssistant, domain: str, service: str, schema: dict[str, Any]
 ) -> None:
     """Register a description for a service."""
+    domain = domain.lower()
+    service = service.lower()
+
     descriptions_cache: dict[
         tuple[str, str], dict[str, Any] | None
     ] = hass.data.setdefault(SERVICE_DESCRIPTION_CACHE, {})
diff --git a/tests/helpers/test_service.py b/tests/helpers/test_service.py
index 6adec334bb0..36f87b7553b 100644
--- a/tests/helpers/test_service.py
+++ b/tests/helpers/test_service.py
@@ -724,6 +724,27 @@ async def test_async_get_all_descriptions_dynamically_created_services(
     }
 
 
+async def test_register_with_mixed_case(hass: HomeAssistant) -> None:
+    """Test registering a service with mixed case.
+
+    For backwards compatibility, we have historically allowed mixed case,
+    and automatically converted it to lowercase.
+    """
+    logger = hass.components.logger
+    logger_config = {logger.DOMAIN: {}}
+    await async_setup_component(hass, logger.DOMAIN, logger_config)
+    logger_domain_mixed = "LoGgEr"
+    hass.services.async_register(
+        logger_domain_mixed, "NeW_SeRVICE", lambda x: None, None
+    )
+    service.async_set_service_schema(
+        hass, logger_domain_mixed, "NeW_SeRVICE", {"description": "new service"}
+    )
+    descriptions = await service.async_get_all_descriptions(hass)
+    assert "description" in descriptions[logger.DOMAIN]["new_service"]
+    assert descriptions[logger.DOMAIN]["new_service"]["description"] == "new service"
+
+
 async def test_call_with_required_features(hass: HomeAssistant, mock_entities) -> None:
     """Test service calls invoked only if entity has required features."""
     test_service_mock = AsyncMock(return_value=None)