diff --git a/packages/app-defaults/src/defaults/apis.ts b/packages/app-defaults/src/defaults/apis.ts
index 3f5cfc1c58..c53ce63ada 100644
--- a/packages/app-defaults/src/defaults/apis.ts
+++ b/packages/app-defaults/src/defaults/apis.ts
@@ -64,10 +64,19 @@ export const apis = [
   createApiFactory({
     api: discoveryApiRef,
     deps: { configApi: configApiRef },
-    factory: ({ configApi }) =>
-      UrlPatternDiscovery.compile(
-        `${configApi.getString('backend.baseUrl')}/api/{{ pluginId }}`,
-      ),
+    factory: ({ configApi }) => {
+      let baseUrl;
+      try {
+        // Try parsing the url relative to the current document origin, if it fails the URL is misformed.
+        baseUrl = new URL(
+          configApi.getString('backend.baseUrl'),
+          document.location.origin,
+        ).href.replace(/\/$/, '');
+      } catch (err) {
+        baseUrl = configApi.getString('backend.baseUrl');
+      }
+      return UrlPatternDiscovery.compile(`${baseUrl}/api/{{ pluginId }}`);
+    },
   }),
   createApiFactory({
     api: alertApiRef,
diff --git a/packages/cli/src/commands/build/buildFrontend.ts b/packages/cli/src/commands/build/buildFrontend.ts
index 6d7ca2e6a9..7f1687ca03 100644
--- a/packages/cli/src/commands/build/buildFrontend.ts
+++ b/packages/cli/src/commands/build/buildFrontend.ts
@@ -19,15 +19,17 @@ import { resolve as resolvePath } from 'path';
 import { buildBundle } from '../../lib/bundler';
 import { getEnvironmentParallelism } from '../../lib/parallel';
 import { loadCliConfig } from '../../lib/config';
+import { CliConfigOptions } from '@backstage/config-loader/src/lib/cli';
 
 interface BuildAppOptions {
   targetDir: string;
   writeStats: boolean;
+  cliOptions?: CliConfigOptions;
   configPaths: string[];
 }
 
 export async function buildFrontend(options: BuildAppOptions) {
-  const { targetDir, writeStats, configPaths } = options;
+  const { targetDir, writeStats, configPaths, cliOptions } = options;
   const { name } = await fs.readJson(resolvePath(targetDir, 'package.json'));
   await buildBundle({
     targetDir,
@@ -37,6 +39,7 @@ export async function buildFrontend(options: BuildAppOptions) {
     ...(await loadCliConfig({
       args: configPaths,
       fromPackage: name,
+      cliOptions,
     })),
   });
 }
diff --git a/packages/cli/src/commands/index.ts b/packages/cli/src/commands/index.ts
index 82cb60e62f..33291cb70c 100644
--- a/packages/cli/src/commands/index.ts
+++ b/packages/cli/src/commands/index.ts
@@ -39,6 +39,14 @@ export function registerRepoCommand(program: Command) {
       '--all',
       'Build all packages, including bundled app and backend packages.',
     )
+    .option(
+      '--public-path <path>',
+      'Public path for hosting the website on, can be relative.',
+    )
+    .option(
+      '--backend-url <url>',
+      'Backend url, expects just the origin or sub-route. Do not include /api. Can be relative.',
+    )
     .option(
       '--since <ref>',
       'Only build packages and their dev dependents that changed since the specified ref',
diff --git a/packages/cli/src/commands/repo/build.ts b/packages/cli/src/commands/repo/build.ts
index 21b1580cb9..86d2e781a6 100644
--- a/packages/cli/src/commands/repo/build.ts
+++ b/packages/cli/src/commands/repo/build.ts
@@ -153,6 +153,10 @@ export async function command(opts: OptionValues, cmd: Command): Promise<void> {
           return;
         }
         await buildFrontend({
+          cliOptions: {
+            publicPath: opts.publicPath,
+            backendUrl: opts.backendUrl,
+          },
           targetDir: pkg.dir,
           configPaths: (buildOptions.config as string[]) ?? [],
           writeStats: Boolean(buildOptions.stats),
diff --git a/packages/cli/src/lib/bundler/config.ts b/packages/cli/src/lib/bundler/config.ts
index 1974153f02..bc0ff2db3b 100644
--- a/packages/cli/src/lib/bundler/config.ts
+++ b/packages/cli/src/lib/bundler/config.ts
@@ -36,10 +36,12 @@ import { runPlain } from '../run';
 import ESLintPlugin from 'eslint-webpack-plugin';
 import pickBy from 'lodash/pickBy';
 
+const DUMMY_URL = 'http://dummyurl.org';
+
 export function resolveBaseUrl(config: Config): URL {
   const baseUrl = config.getString('app.baseUrl');
   try {
-    return new URL(baseUrl);
+    return new URL(baseUrl, DUMMY_URL);
   } catch (error) {
     throw new Error(`Invalid app.baseUrl, ${error}`);
   }
@@ -88,7 +90,7 @@ export async function createConfig(
   const externalPkgs = packages.filter(p => !isChildPath(paths.root, p.dir));
 
   const baseUrl = frontendConfig.getString('app.baseUrl');
-  const validBaseUrl = new URL(baseUrl);
+  const validBaseUrl = new URL(baseUrl, DUMMY_URL);
   const publicPath = validBaseUrl.pathname.replace(/\/$/, '');
   if (checksEnabled) {
     plugins.push(
diff --git a/packages/cli/src/lib/bundler/server.ts b/packages/cli/src/lib/bundler/server.ts
index fb11316fa6..1e76fbc662 100644
--- a/packages/cli/src/lib/bundler/server.ts
+++ b/packages/cli/src/lib/bundler/server.ts
@@ -60,6 +60,9 @@ export async function serveBundle(options: ServeOptions) {
         // Paths with dots should still use the history fallback.
         // See https://github.com/facebookincubator/create-react-app/issues/387.
         disableDotRule: true,
+
+        // The index needs to be rewritten relative to the new public path, including subroutes.
+        index: config.output?.publicPath ?? '/index.html',
       },
       https:
         url.protocol === 'https:'
diff --git a/packages/cli/src/lib/config.ts b/packages/cli/src/lib/config.ts
index a76571c3f6..e28f2d7f6f 100644
--- a/packages/cli/src/lib/config.ts
+++ b/packages/cli/src/lib/config.ts
@@ -32,6 +32,10 @@ type Options = {
   withFilteredKeys?: boolean;
   withDeprecatedKeys?: boolean;
   fullVisibility?: boolean;
+  cliOptions?: {
+    publicPath?: string;
+    backendUrl?: string;
+  };
 };
 
 export async function loadCliConfig(options: Options) {
@@ -76,6 +80,7 @@ export async function loadCliConfig(options: Options) {
     experimentalEnvFunc: options.mockEnv
       ? async name => process.env[name] || 'x'
       : undefined,
+    cliOptions: options.cliOptions,
     configRoot: paths.targetRoot,
     configTargets: configTargets,
   });
diff --git a/packages/config-loader/src/lib/cli.ts b/packages/config-loader/src/lib/cli.ts
new file mode 100644
index 0000000000..9d935e2826
--- /dev/null
+++ b/packages/config-loader/src/lib/cli.ts
@@ -0,0 +1,49 @@
+/*
+ * Copyright 2022 The Backstage Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import { AppConfig } from '@backstage/config';
+import { JsonObject } from '@backstage/types';
+
+export type CliConfigOptions = {
+  publicPath?: string;
+  backendUrl?: string;
+};
+
+/**
+ * Read specific parameters from the CLI and add them to the build config.
+ * @param opts CLI passed parameters.
+ * @returns Array of config, empty if there is no relevant passed in cli options.
+ *
+ * @public
+ */
+export function readCliConfig(opts?: CliConfigOptions): AppConfig[] {
+  if (!opts || Object.keys(opts).length === 0) return [];
+  const data: JsonObject = {};
+
+  if (opts.publicPath) {
+    data.app = {
+      baseUrl: opts.publicPath,
+    };
+  }
+
+  if (opts.backendUrl) {
+    data.backend = {
+      baseUrl: opts.backendUrl,
+    };
+  }
+
+  return [{ data, context: 'cli' }];
+}
diff --git a/packages/config-loader/src/loader.ts b/packages/config-loader/src/loader.ts
index f5ce0eb80c..44bd4f94e8 100644
--- a/packages/config-loader/src/loader.ts
+++ b/packages/config-loader/src/loader.ts
@@ -28,6 +28,7 @@ import {
   readEnvConfig,
 } from './lib';
 import fetch from 'node-fetch';
+import { CliConfigOptions, readCliConfig } from './lib/cli';
 
 /** @public */
 export type ConfigTarget = { path: string } | { url: string };
@@ -81,6 +82,11 @@ export type LoadConfigOptions = {
    * An optional configuration that enables watching of config files.
    */
   watch?: LoadConfigOptionsWatch;
+
+  /**
+   * New options from the CLI that affect the build config.
+   */
+  cliOptions?: CliConfigOptions;
 };
 
 /**
@@ -230,6 +236,8 @@ export async function loadConfig(
     }
   }
 
+  const cliConfigs = readCliConfig(options.cliOptions);
+
   const envConfigs = readEnvConfig(process.env);
 
   const watchConfigFile = (watchProp: LoadConfigOptionsWatch) => {
@@ -318,7 +326,7 @@ export async function loadConfig(
 
   return {
     appConfigs: remote
-      ? [...remoteConfigs, ...fileConfigs, ...envConfigs]
-      : [...fileConfigs, ...envConfigs],
+      ? [...remoteConfigs, ...fileConfigs, ...envConfigs, ...cliConfigs]
+      : [...fileConfigs, ...envConfigs, ...cliConfigs],
   };
 }
diff --git a/packages/core-app-api/src/app/AppManager.tsx b/packages/core-app-api/src/app/AppManager.tsx
index 0ca09c0a0c..9b3dc841d0 100644
--- a/packages/core-app-api/src/app/AppManager.tsx
+++ b/packages/core-app-api/src/app/AppManager.tsx
@@ -116,7 +116,7 @@ function getBasePath(configApi: Config) {
 function readBasePath(configApi: ConfigApi) {
   let { pathname } = new URL(
     configApi.getOptionalString('app.baseUrl') ?? '/',
-    'http://dummy.dev', // baseUrl can be specified as just a path
+    document.location.origin, // baseUrl can be specified as just a path
   );
   pathname = pathname.replace(/\/*$/, '');
   return pathname;
@@ -332,7 +332,6 @@ export class AppManager implements BackstageApp {
                 routeParents={routing.parents}
                 routeObjects={routing.objects}
                 routeBindings={routeBindings}
-                basePath={getBasePath(loadedConfig.api)}
               >
                 <InternalAppContext.Provider
                   value={{ routeObjects: routing.objects }}
@@ -426,7 +425,7 @@ export class AppManager implements BackstageApp {
 
       if (isReactRouterBeta()) {
         return (
-          <RouterComponent>
+          <RouterComponent basename={basePath}>
             <RouteTracker routeObjects={routeObjects} />
             <SignInPageWrapper component={SignInPageComponent}>
               <Routes>
diff --git a/packages/core-app-api/src/app/types.ts b/packages/core-app-api/src/app/types.ts
index 70022534a1..b548533df3 100644
--- a/packages/core-app-api/src/app/types.ts
+++ b/packages/core-app-api/src/app/types.ts
@@ -60,6 +60,10 @@ export type ErrorBoundaryFallbackProps = {
   resetError: () => void;
 };
 
+export type RouterProps = {
+  basename: string;
+};
+
 /**
  * A set of replaceable core components that are part of every Backstage app.
  *
diff --git a/packages/core-app-api/src/routing/RouteResolver.ts b/packages/core-app-api/src/routing/RouteResolver.ts
index f17c549bc6..1b23aa30f1 100644
--- a/packages/core-app-api/src/routing/RouteResolver.ts
+++ b/packages/core-app-api/src/routing/RouteResolver.ts
@@ -214,15 +214,13 @@ export class RouteResolver {
     // Next we figure out the base path, which is the combination of the common parent path
     // between our current location and our target location, as well as the additional path
     // that is the difference between the parent path and the base of our target location.
-    const basePath =
-      this.appBasePath +
-      resolveBasePath(
-        targetRef,
-        relativeSourceLocation,
-        this.routePaths,
-        this.routeParents,
-        this.routeObjects,
-      );
+    const basePath = resolveBasePath(
+      targetRef,
+      relativeSourceLocation,
+      this.routePaths,
+      this.routeParents,
+      this.routeObjects,
+    );
 
     const routeFunc: RouteFunc<Params> = (...[params]) => {
       return joinPaths(basePath, generatePath(targetPath, params));