diff --git a/README.rst b/README.rst
index 6eff907a3..7ccbb76a7 100644
--- a/README.rst
+++ b/README.rst
@@ -325,6 +325,20 @@ switch to the REST client by setting the ``SOPS_GCP_KMS_CLIENT_TYPE`` environmen
     $ export SOPS_GCP_KMS_CLIENT_TYPE=rest  # Use REST client
     $ export SOPS_GCP_KMS_CLIENT_TYPE=grpc  # Use gRPC client (default)
 
+For sovereign cloud environments that expose a GCP-compatible KMS API at a
+non-standard endpoint (e.g. S3NS/Thales TPC: ``cloudkms.s3nsapis.fr``),
+you can override the endpoint or the universe domain:
+
+.. code:: sh
+
+    # Override the KMS endpoint directly
+    $ export SOPS_GCP_KMS_ENDPOINT=cloudkms.example.com:443
+
+    # Or derive the endpoint from the universe domain (cloudkms.<domain>:443)
+    $ export SOPS_GCP_KMS_UNIVERSE_DOMAIN=example.com
+
+.. note:: ``SOPS_GCP_KMS_ENDPOINT`` takes precedence over ``SOPS_GCP_KMS_UNIVERSE_DOMAIN`` if both are set.
+
 Encrypting/decrypting with GCP KMS requires a KMS ResourceID. You can use the
 cloud console the get the ResourceID or you can create one using the gcloud
 sdk:
diff --git a/gcpkms/keysource.go b/gcpkms/keysource.go
index d9cc55089..2acbdd9c0 100644
--- a/gcpkms/keysource.go
+++ b/gcpkms/keysource.go
@@ -30,6 +30,14 @@ const (
 	// SopsGCPKMSClientTypeEnv is the environment variable used to specify the
 	// GCP KMS client type. Valid values are "grpc" (default) and "rest".
 	SopsGCPKMSClientTypeEnv = "SOPS_GCP_KMS_CLIENT_TYPE"
+	// SopsGCPKMSEndpointEnv overrides the GCP KMS endpoint URL. Useful for
+	// sovereign cloud environments that expose a GCP-compatible KMS API at a
+	// non-standard endpoint (e.g. S3NS/Thales TPC: cloudkms.s3nsapis.fr).
+	SopsGCPKMSEndpointEnv = "SOPS_GCP_KMS_ENDPOINT"
+	// SopsGCPKMSUniverseDomainEnv sets the universe domain for the GCP KMS
+	// client, which derives the endpoint as cloudkms.{UNIVERSE_DOMAIN}:443.
+	// Example: "s3nsapis.fr" for S3NS/Thales TPC.
+	SopsGCPKMSUniverseDomainEnv = "SOPS_GCP_KMS_UNIVERSE_DOMAIN"
 	// KeyTypeIdentifier is the string used to identify a GCP KMS MasterKey.
 	KeyTypeIdentifier = "gcp_kms"
 )
@@ -320,6 +328,12 @@ func (key *MasterKey) newKMSClient(ctx context.Context) (*kms.KeyManagementClien
 	// Add extra options.
 	opts = append(opts, key.clientOpts...)
 
+	if endpoint := os.Getenv(SopsGCPKMSEndpointEnv); endpoint != "" {
+		opts = append(opts, option.WithEndpoint(endpoint))
+	} else if ud := os.Getenv(SopsGCPKMSUniverseDomainEnv); ud != "" {
+		opts = append(opts, option.WithUniverseDomain(ud))
+	}
+
 	// Select client type based on inputs.
 	clientType := strings.ToLower(os.Getenv(SopsGCPKMSClientTypeEnv))
 	var client *kms.KeyManagementClient
diff --git a/gcpkms/keysource_test.go b/gcpkms/keysource_test.go
index e0365de34..fa50b6bb8 100644
--- a/gcpkms/keysource_test.go
+++ b/gcpkms/keysource_test.go
@@ -189,6 +189,32 @@ func TestMasterKey_createCloudKMSService_withoutCredentials(t *testing.T) {
 	assert.ErrorContains(t, err, "credentials: could not find default credentials")
 }
 
+func TestMasterKey_createCloudKMSService_withEndpointEnv(t *testing.T) {
+	t.Setenv(SopsGCPKMSEndpointEnv, "cloudkms.example.com:443")
+	t.Setenv(SopsGoogleCredentialsOAuthTokenEnv, "token")
+
+	masterKey := MasterKey{
+		ResourceID: testResourceID,
+	}
+
+	client, err := masterKey.newKMSClient(context.Background())
+	assert.NoError(t, err)
+	assert.Contains(t, client.Connection().Target(), "cloudkms.example.com")
+}
+
+func TestMasterKey_createCloudKMSService_withUniverseDomainEnv(t *testing.T) {
+	t.Setenv(SopsGCPKMSUniverseDomainEnv, "example.com")
+	t.Setenv(SopsGoogleCredentialsOAuthTokenEnv, "token")
+
+	masterKey := MasterKey{
+		ResourceID: testResourceID,
+	}
+
+	client, err := masterKey.newKMSClient(context.Background())
+	assert.NoError(t, err)
+	assert.Contains(t, client.Connection().Target(), "cloudkms.example.com")
+}
+
 func newGRPCServer(port string) *grpc.ClientConn {
 	serv := grpc.NewServer()
 	kmspb.RegisterKeyManagementServiceServer(serv, &mockKeyManagement)