diff --git a/app/runtime/server/setup/prerequisites.py b/app/runtime/server/setup/prerequisites.py
index 5b2a1fd..f08d73a 100644
--- a/app/runtime/server/setup/prerequisites.py
+++ b/app/runtime/server/setup/prerequisites.py
@@ -89,6 +89,9 @@ async def deploy(self, req: web.Request) -> web.Response:
                 "message": "Key Vault already configured",
             })
 
+        if not await self._register_keyvault_provider(steps):
+            return _fail(steps)
+
         if not await self._ensure_rg(prereq_rg, location, steps):
             return _fail(steps)
 
@@ -133,6 +136,9 @@ async def ensure_keyvault_ready(
 
         prereq_rg = _DEFAULT_PREREQ_RG
 
+        if not await self._register_keyvault_provider(steps):
+            return steps
+
         if not await self._ensure_rg(prereq_rg, location, steps):
             return steps
 
@@ -144,6 +150,19 @@ async def ensure_keyvault_ready(
         await self._wait_for_access(steps)
         return steps
 
+    async def _register_keyvault_provider(self, steps: list[dict]) -> bool:
+        """Register the Microsoft.KeyVault resource provider on the active subscription."""
+        ok, msg = await run_sync(
+            self._az.ok,
+            "provider", "register", "--namespace", "Microsoft.KeyVault", "--wait",
+        )
+        steps.append({
+            "step": "provider_registration",
+            "status": "ok" if ok else "failed",
+            "detail": "Microsoft.KeyVault registered" if ok else (msg or "Unknown error"),
+        })
+        return ok
+
     def _link_existing_keyvault(self) -> None:
         """Ensure the existing Key Vault resource is registered on the current deployment."""
         if not self._deploy_store:
diff --git a/app/runtime/tests/test_prerequisites.py b/app/runtime/tests/test_prerequisites.py
index a80f3c7..e078fa6 100644
--- a/app/runtime/tests/test_prerequisites.py
+++ b/app/runtime/tests/test_prerequisites.py
@@ -1,4 +1,4 @@
-"""Tests for PrerequisitesRoutes._link_existing_keyvault."""
+"""Tests for PrerequisitesRoutes helpers."""
 
 from __future__ import annotations
 
@@ -7,15 +7,17 @@
 
 from app.runtime.config.settings import cfg
 from app.runtime.server.setup.prerequisites import PrerequisitesRoutes
-from app.runtime.state.deploy_state import DeployStateStore, DeploymentRecord
+from app.runtime.state.deploy_state import DeploymentRecord, DeployStateStore
 from app.runtime.state.infra_config import InfraConfigStore
+from app.runtime.util.result import Result
 
 
 def _make_routes(
     tmp_path: Path,
     deploy_store: DeployStateStore | None = None,
+    az: MagicMock | None = None,
 ) -> PrerequisitesRoutes:
-    az = MagicMock()
+    az = az or MagicMock()
     store = InfraConfigStore(path=tmp_path / "infra.json")
     return PrerequisitesRoutes(az, store, deploy_store=deploy_store)
 
@@ -75,3 +77,36 @@ def test_noop_without_kv_name(self, tmp_path: Path) -> None:
 
         updated = ds.get("cccc3333")
         assert len(updated.resources) == 0
+
+
+class TestRegisterKeyvaultProvider:
+    async def test_success_appends_ok_step(self, tmp_path: Path) -> None:
+        az = MagicMock()
+        az.ok.return_value = Result.ok("Registered")
+        routes = _make_routes(tmp_path, az=az)
+
+        steps: list[dict] = []
+        result = await routes._register_keyvault_provider(steps)
+
+        assert result is True
+        assert len(steps) == 1
+        assert steps[0]["step"] == "provider_registration"
+        assert steps[0]["status"] == "ok"
+        assert "Microsoft.KeyVault" in steps[0]["detail"]
+        az.ok.assert_called_once_with(
+            "provider", "register", "--namespace", "Microsoft.KeyVault", "--wait",
+        )
+
+    async def test_failure_appends_failed_step(self, tmp_path: Path) -> None:
+        az = MagicMock()
+        az.ok.return_value = Result.fail("Subscription not found")
+        routes = _make_routes(tmp_path, az=az)
+
+        steps: list[dict] = []
+        result = await routes._register_keyvault_provider(steps)
+
+        assert result is False
+        assert len(steps) == 1
+        assert steps[0]["step"] == "provider_registration"
+        assert steps[0]["status"] == "failed"
+        assert "Subscription not found" in steps[0]["detail"]