diff --git a/src/core/ext/xds/xds_bootstrap.cc b/src/core/ext/xds/xds_bootstrap.cc
index e48d9827dec..95f4c3de1e3 100644
--- a/src/core/ext/xds/xds_bootstrap.cc
+++ b/src/core/ext/xds/xds_bootstrap.cc
@@ -132,13 +132,40 @@ std::string BootstrapString(const XdsBootstrap& bootstrap) {
   return absl::StrJoin(parts, "");
 }
 
+std::unique_ptr<XdsBootstrap> ParseJsonAndCreate(
+    XdsClient* client, TraceFlag* tracer, absl::string_view json_string,
+    absl::string_view bootstrap_source, grpc_error** error) {
+  Json json = Json::Parse(json_string, error);
+  if (*error != GRPC_ERROR_NONE) {
+    grpc_error* error_out = GRPC_ERROR_CREATE_REFERENCING_FROM_COPIED_STRING(
+        absl::StrCat("Failed to parse bootstrap from ", bootstrap_source)
+            .c_str(),
+        error, 1);
+    GRPC_ERROR_UNREF(*error);
+    *error = error_out;
+    return nullptr;
+  }
+  std::unique_ptr<XdsBootstrap> result =
+      absl::make_unique<XdsBootstrap>(std::move(json), error);
+  if (*error == GRPC_ERROR_NONE && GRPC_TRACE_FLAG_ENABLED(*tracer)) {
+    gpr_log(GPR_INFO,
+            "[xds_client %p] Bootstrap config for creating xds client:\n%s",
+            client, BootstrapString(*result).c_str());
+  }
+  return result;
+}
+
 }  // namespace
 
-std::unique_ptr<XdsBootstrap> XdsBootstrap::ReadFromFile(XdsClient* client,
-                                                         TraceFlag* tracer,
-                                                         grpc_error** error) {
+std::unique_ptr<XdsBootstrap> XdsBootstrap::ReadFromFile(
+    XdsClient* client, TraceFlag* tracer, const char* fallback_config,
+    grpc_error** error) {
   grpc_core::UniquePtr<char> path(gpr_getenv("GRPC_XDS_BOOTSTRAP"));
   if (path == nullptr) {
+    if (fallback_config != nullptr) {
+      return ParseJsonAndCreate(client, tracer, fallback_config,
+                                "fallback config", error);
+    }
     *error = GRPC_ERROR_CREATE_FROM_STATIC_STRING(
         "Environment variable GRPC_XDS_BOOTSTRAP not defined");
     return nullptr;
@@ -157,23 +184,10 @@ std::unique_ptr<XdsBootstrap> XdsBootstrap::ReadFromFile(XdsClient* client,
     gpr_log(GPR_DEBUG, "[xds_client %p] Bootstrap file contents: %s", client,
             std::string(contents_str_view).c_str());
   }
-  Json json = Json::Parse(contents_str_view, error);
+  std::string bootstrap_source = absl::StrCat("file ", path.get());
+  auto result = ParseJsonAndCreate(client, tracer, contents_str_view,
+                                   bootstrap_source, error);
   grpc_slice_unref_internal(contents);
-  if (*error != GRPC_ERROR_NONE) {
-    grpc_error* error_out = GRPC_ERROR_CREATE_REFERENCING_FROM_COPIED_STRING(
-        absl::StrCat("Failed to parse bootstrap file ", path.get()).c_str(),
-        error, 1);
-    GRPC_ERROR_UNREF(*error);
-    *error = error_out;
-    return nullptr;
-  }
-  std::unique_ptr<XdsBootstrap> result =
-      absl::make_unique<XdsBootstrap>(std::move(json), error);
-  if (*error == GRPC_ERROR_NONE && GRPC_TRACE_FLAG_ENABLED(*tracer)) {
-    gpr_log(GPR_INFO,
-            "[xds_client %p] Bootstrap config for creating xds client:\n%s",
-            client, BootstrapString(*result).c_str());
-  }
   return result;
 }
 
diff --git a/src/core/ext/xds/xds_bootstrap.h b/src/core/ext/xds/xds_bootstrap.h
index 969d5d54992..5d1f9095858 100644
--- a/src/core/ext/xds/xds_bootstrap.h
+++ b/src/core/ext/xds/xds_bootstrap.h
@@ -67,10 +67,13 @@ class XdsBootstrap {
     bool ShouldUseV3() const;
   };
 
+  // Normally locates the bootstrap file via an env var.  If no env var
+  // is set, fallback_config will be used instead (if non-null).
   // If *error is not GRPC_ERROR_NONE after returning, then there was an
   // error reading the file.
   static std::unique_ptr<XdsBootstrap> ReadFromFile(XdsClient* client,
                                                     TraceFlag* tracer,
+                                                    const char* fallback_config,
                                                     grpc_error** error);
 
   // Do not instantiate directly -- use ReadFromFile() above instead.
diff --git a/src/core/ext/xds/xds_client.cc b/src/core/ext/xds/xds_client.cc
index b31bbbdc1f1..e95cf7aa663 100644
--- a/src/core/ext/xds/xds_client.cc
+++ b/src/core/ext/xds/xds_client.cc
@@ -72,6 +72,7 @@ namespace {
 Mutex* g_mu = nullptr;
 const grpc_channel_args* g_channel_args = nullptr;
 XdsClient* g_xds_client = nullptr;
+char* g_fallback_bootstrap_config = nullptr;
 
 }  // namespace
 
@@ -1740,8 +1741,8 @@ XdsClient::XdsClient(grpc_error** error)
                                                                   : nullptr),
       request_timeout_(GetRequestTimeout()),
       interested_parties_(grpc_pollset_set_create()),
-      bootstrap_(
-          XdsBootstrap::ReadFromFile(this, &grpc_xds_client_trace, error)),
+      bootstrap_(XdsBootstrap::ReadFromFile(
+          this, &grpc_xds_client_trace, g_fallback_bootstrap_config, error)),
       certificate_provider_store_(MakeOrphanable<CertificateProviderStore>(
           bootstrap_ == nullptr
               ? CertificateProviderStore::PluginDefinitionMap()
@@ -2207,6 +2208,8 @@ void XdsClientGlobalInit() { g_mu = new Mutex; }
 void XdsClientGlobalShutdown() {
   delete g_mu;
   g_mu = nullptr;
+  gpr_free(g_fallback_bootstrap_config);
+  g_fallback_bootstrap_config = nullptr;
 }
 
 RefCountedPtr<XdsClient> XdsClient::GetOrCreate(grpc_error** error) {
@@ -2232,6 +2235,12 @@ void UnsetGlobalXdsClientForTest() {
   g_xds_client = nullptr;
 }
 
+void SetXdsFallbackBootstrapConfig(char* config) {
+  MutexLock lock(g_mu);
+  gpr_free(g_fallback_bootstrap_config);
+  g_fallback_bootstrap_config = config;
+}
+
 }  // namespace internal
 
 }  // namespace grpc_core
diff --git a/src/core/ext/xds/xds_client.h b/src/core/ext/xds/xds_client.h
index f1c6467556c..791b3990376 100644
--- a/src/core/ext/xds/xds_client.h
+++ b/src/core/ext/xds/xds_client.h
@@ -329,6 +329,9 @@ class XdsClient : public DualRefCounted<XdsClient> {
 namespace internal {
 void SetXdsChannelArgsForTest(grpc_channel_args* args);
 void UnsetGlobalXdsClientForTest();
+// Sets bootstrap config to be used when no env var is set.
+// Takes ownership of config.
+void SetXdsFallbackBootstrapConfig(char* config);
 }  // namespace internal
 
 }  // namespace grpc_core