diff --git a/neutron/conf/agent/l3/config.py b/neutron/conf/agent/l3/config.py
index 3344ed756bc..1331fcd648d 100644
--- a/neutron/conf/agent/l3/config.py
+++ b/neutron/conf/agent/l3/config.py
@@ -60,7 +60,8 @@ OPTS = [
                       "This value should be set to the UUID of that external "
                       "network. To allow L3 agent support multiple external "
                       "networks, both the external_network_bridge and "
-                      "gateway_external_network_id must be left empty.")),
+                      "gateway_external_network_id must be left empty."),
+               deprecated_for_removal=True),
     cfg.StrOpt('ipv6_gateway', default='',
                help=_("With IPv6, the network used for the external gateway "
                       "does not need to have an associated subnet, since the "
diff --git a/releasenotes/notes/deprecate-gateway_external_network_id-f5c4071cd06714b0.yaml b/releasenotes/notes/deprecate-gateway_external_network_id-f5c4071cd06714b0.yaml
new file mode 100644
index 00000000000..7f37091e9a5
--- /dev/null
+++ b/releasenotes/notes/deprecate-gateway_external_network_id-f5c4071cd06714b0.yaml
@@ -0,0 +1,5 @@
+---
+deprecations:
+  - The ``gateway_external_network_id`` L3 agent option is deprecated and will
+    be removed in next releases, with ``external_network_bridge`` that it
+    depends on.