diff --git a/changelog.d/19056.misc b/changelog.d/19056.misc
new file mode 100644
index 00000000000..f3a1b4e66ea
--- /dev/null
+++ b/changelog.d/19056.misc
@@ -0,0 +1 @@
+Move `oidc.load_metadata()` startup into `_base.start()`.
diff --git a/synapse/app/_base.py b/synapse/app/_base.py
index b416b66ac6e..6bb1fb114b6 100644
--- a/synapse/app/_base.py
+++ b/synapse/app/_base.py
@@ -625,6 +625,16 @@ def run_sighup(*args: Any, **kwargs: Any) -> None:
     # Apply the cache config.
     hs.config.caches.resize_all_caches()
 
+    # Load the OIDC provider metadatas, if OIDC is enabled.
+    if hs.config.oidc.oidc_enabled:
+        oidc = hs.get_oidc_handler()
+        # Loading the provider metadata also ensures the provider config is valid.
+        #
+        # FIXME: It feels a bit strange to validate and block on startup as one of these
+        # OIDC providers could be temporarily unavailable and cause Synapse to be unable
+        # to start.
+        await oidc.load_metadata()
+
     # Load the certificate from disk.
     refresh_certificate(hs)
 
diff --git a/synapse/app/homeserver.py b/synapse/app/homeserver.py
index b9ac86c2fc3..b1fa4e2ec7c 100644
--- a/synapse/app/homeserver.py
+++ b/synapse/app/homeserver.py
@@ -425,13 +425,12 @@ def setup(
         handle_startup_exception(e)
 
     async def _start_when_reactor_running() -> None:
-        # TODO: Feels like this should be moved somewhere else.
-        #
-        # Load the OIDC provider metadatas, if OIDC is enabled.
-        if hs.config.oidc.oidc_enabled:
-            oidc = hs.get_oidc_handler()
-            # Loading the provider metadata also ensures the provider config is valid.
-            await oidc.load_metadata()
+        """
+        Things that should run when starting the `SynapseHomeServer` (main homeserver
+        process) should live here.
+
+        Should be called once the reactor is running.
+        """
 
         await _base.start(hs, freeze)