diff --git a/news/changelog-1.9.md b/news/changelog-1.9.md
index 894773bce7d..4163bd44de8 100644
--- a/news/changelog-1.9.md
+++ b/news/changelog-1.9.md
@@ -33,6 +33,7 @@ All changes included in 1.9:
 - ([#11929](https://github.com/quarto-dev/quarto-cli/issues/11929)): Import all `brand.typography.fonts` in CSS, whether or not fonts are referenced by typography elements.
 - ([#13413](https://github.com/quarto-dev/quarto-cli/issues/13413)): Fix uncentered play button in `video` shortcodes from cross-reference divs. (author: @bruvellu)
 - ([#13508](https://github.com/quarto-dev/quarto-cli/issues/13508)): Add `aria-label` support to `video` shortcode for improved accessibility.
+- ([#13685](https://github.com/quarto-dev/quarto-cli/issues/13685)): Fix remote font URLs in brand extensions being incorrectly joined with the extension path, resulting in broken font imports.
 
 ### `typst`
 
diff --git a/src/core/brand/brand.ts b/src/core/brand/brand.ts
index 38c1d0c80ca..19e545a67e4 100644
--- a/src/core/brand/brand.ts
+++ b/src/core/brand/brand.ts
@@ -32,6 +32,7 @@ import { InternalError } from "../lib/error.ts";
 import { dirname, join, relative, resolve } from "../../deno_ral/path.ts";
 import { warnOnce } from "../log.ts";
 import { isCssColorName } from "../css/color-names.ts";
+import { isExternalPath } from "../url.ts";
 import {
   LogoLightDarkSpecifierPathOptional,
   LogoOptionsPathOptional,
@@ -272,10 +273,6 @@ export class Brand {
   }
 }
 
-function isExternalPath(path: string) {
-  return /^\w+:/.test(path);
-}
-
 export type LightDarkBrand = {
   light?: Brand;
   dark?: Brand;
diff --git a/src/core/sass/brand.ts b/src/core/sass/brand.ts
index 993fb5eac0a..07f4695aea8 100644
--- a/src/core/sass/brand.ts
+++ b/src/core/sass/brand.ts
@@ -26,6 +26,7 @@ import { Brand } from "../brand/brand.ts";
 import { darkModeDefault } from "../../format/html/format-html-info.ts";
 import { kBrandMode } from "../../config/constants.ts";
 import { join, relative } from "../../deno_ral/path.ts";
+import { isExternalPath } from "../url.ts";
 
 const defaultColorNameMap: Record<string, string> = {
   "link-color": "link",
@@ -162,9 +163,12 @@ const fileFontImportString = (brand: Brand, description: BrandFontFile) => {
       weight = file.weight;
       style = file.style;
     }
+    const fontUrl = isExternalPath(path)
+      ? path
+      : join(pathPrefix, path).replace(/\\/g, "/");
     parts.push(`@font-face {
     font-family: '${description.family}';
-    src: url('${join(pathPrefix, path).replace(/\\/g, "/")}');
+    src: url('${fontUrl}');
     font-weight: ${weight || "normal"};
     font-style: ${style || "normal"};
 }\n`);
diff --git a/src/core/url.ts b/src/core/url.ts
index a07ac222f70..2b3c5caf714 100644
--- a/src/core/url.ts
+++ b/src/core/url.ts
@@ -1,9 +1,8 @@
 /*
-* url.ts
-*
-* Copyright (C) 2020-2022 Posit Software, PBC
-*
-*/
+ * url.ts
+ *
+ * Copyright (C) 2020-2022 Posit Software, PBC
+ */
 
 import { ensureTrailingSlash, pathWithForwardSlashes } from "./path.ts";
 
@@ -11,6 +10,10 @@ export function isHttpUrl(url: string) {
   return /^https?:/i.test(url);
 }
 
+export function isExternalPath(path: string) {
+  return /^\w+:/.test(path);
+}
+
 export function joinUrl(baseUrl: string, path: string) {
   const baseHasSlash = baseUrl.endsWith("/");
 
diff --git a/src/project/types/website/website-navigation.ts b/src/project/types/website/website-navigation.ts
index 30ed38da25f..3c55bea6008 100644
--- a/src/project/types/website/website-navigation.ts
+++ b/src/project/types/website/website-navigation.ts
@@ -12,6 +12,7 @@ import { Document, Element } from "../../../core/deno-dom.ts";
 
 import { pathWithForwardSlashes, safeExistsSync } from "../../../core/path.ts";
 import { resourcePath } from "../../../core/resources.ts";
+import { isExternalPath } from "../../../core/url.ts";
 import { renderEjs } from "../../../core/ejs.ts";
 import { warnOnce } from "../../../core/log.ts";
 import { asHtmlId } from "../../../core/html.ts";
@@ -1540,10 +1541,6 @@ function navigationDependency(resource: string) {
   };
 }
 
-function isExternalPath(path: string) {
-  return /^\w+:/.test(path);
-}
-
 function resolveNavReferences(
   collection: unknown | Array<unknown> | Record<string, unknown>,
 ) {
diff --git a/src/project/types/website/website-utils.ts b/src/project/types/website/website-utils.ts
index 01d42b7c8e4..6aa00f8aadb 100644
--- a/src/project/types/website/website-utils.ts
+++ b/src/project/types/website/website-utils.ts
@@ -8,6 +8,7 @@ import { Document, Element } from "../../../core/deno-dom.ts";
 import { getDecodedAttribute } from "../../../core/html.ts";
 import { resolveInputTarget } from "../../project-index.ts";
 import { pathWithForwardSlashes, safeExistsSync } from "../../../core/path.ts";
+import { isExternalPath } from "../../../core/url.ts";
 import { projectOffset, projectOutputDir } from "../../project-shared.ts";
 import { engineValidExtensions } from "../../../execute/engine.ts";
 import { ProjectContext } from "../../types.ts";
@@ -119,7 +120,3 @@ export async function resolveProjectInputLinks(
     }
   }
 }
-
-function isExternalPath(path: string) {
-  return /^\w+:/.test(path);
-}
diff --git a/tests/docs/smoke-all/brand/typography/remote-font-extension/.gitignore b/tests/docs/smoke-all/brand/typography/remote-font-extension/.gitignore
new file mode 100644
index 00000000000..ad293093b07
--- /dev/null
+++ b/tests/docs/smoke-all/brand/typography/remote-font-extension/.gitignore
@@ -0,0 +1,2 @@
+/.quarto/
+**/*.quarto_ipynb
diff --git a/tests/docs/smoke-all/brand/typography/remote-font-extension/_extensions/my-brand/_extension.yml b/tests/docs/smoke-all/brand/typography/remote-font-extension/_extensions/my-brand/_extension.yml
new file mode 100644
index 00000000000..859925eab79
--- /dev/null
+++ b/tests/docs/smoke-all/brand/typography/remote-font-extension/_extensions/my-brand/_extension.yml
@@ -0,0 +1,8 @@
+title: My Brand
+author: Quarto
+version: 1.0.0
+quarto-required: ">=99.9.0"
+contributes:
+  metadata:
+    project:
+      brand: mybrand.yml
diff --git a/tests/docs/smoke-all/brand/typography/remote-font-extension/_extensions/my-brand/mybrand.yml b/tests/docs/smoke-all/brand/typography/remote-font-extension/_extensions/my-brand/mybrand.yml
new file mode 100644
index 00000000000..1f8fcf43c9d
--- /dev/null
+++ b/tests/docs/smoke-all/brand/typography/remote-font-extension/_extensions/my-brand/mybrand.yml
@@ -0,0 +1,8 @@
+typography:
+  fonts:
+    - family: Noto Sans
+      source: file
+      files:
+        - path: https://notofonts.github.io/latin-greek-cyrillic/fonts/NotoSans/unhinted/ttf/NotoSans-Regular.ttf
+  base:
+    family: Noto Sans
diff --git a/tests/docs/smoke-all/brand/typography/remote-font-extension/_quarto.yml b/tests/docs/smoke-all/brand/typography/remote-font-extension/_quarto.yml
new file mode 100644
index 00000000000..f98ff850162
--- /dev/null
+++ b/tests/docs/smoke-all/brand/typography/remote-font-extension/_quarto.yml
@@ -0,0 +1,5 @@
+project:
+  type: default
+format:
+  html:
+    theme: brand
diff --git a/tests/docs/smoke-all/brand/typography/remote-font-extension/remote-font-extension.qmd b/tests/docs/smoke-all/brand/typography/remote-font-extension/remote-font-extension.qmd
new file mode 100644
index 00000000000..25812585524
--- /dev/null
+++ b/tests/docs/smoke-all/brand/typography/remote-font-extension/remote-font-extension.qmd
@@ -0,0 +1,15 @@
+---
+title: Remote Font Extension Test
+_quarto:
+  tests:
+    html:
+      ensureCssRegexMatches:
+        - ['src:url\("https://notofonts\.github\.io/']
+        - ['_extensions/my-brand/https:']
+---
+
+# Remote Font Test
+
+This document tests that remote font URLs in brand extensions are handled correctly (issue #13685).
+
+{{< lipsum 1 >}}
diff --git a/tests/smoke/smoke-all.test.ts b/tests/smoke/smoke-all.test.ts
index b5aaafa6897..b92c9479aff 100644
--- a/tests/smoke/smoke-all.test.ts
+++ b/tests/smoke/smoke-all.test.ts
@@ -18,6 +18,7 @@ import { breakQuartoMd } from "../../src/core/lib/break-quarto-md.ts";
 import { parse } from "../../src/core/yaml.ts";
 import { cleanoutput } from "./render/render.ts";
 import {
+  ensureCssRegexMatches,
   ensureEpubFileRegexMatches,
   ensureDocxRegexMatches,
   ensureDocxXpath,
@@ -171,6 +172,7 @@ function resolveTestSpecs(
   const result = [];
   // deno-lint-ignore no-explicit-any
   const verifyMap: Record<string, any> = {
+    ensureCssRegexMatches,
     ensureEpubFileRegexMatches,
     ensureHtmlElements,
     ensureHtmlElementContents,
diff --git a/tests/verify.ts b/tests/verify.ts
index a38dbbd01d5..cbfdca3836e 100644
--- a/tests/verify.ts
+++ b/tests/verify.ts
@@ -5,7 +5,7 @@
  */
 
 import { existsSync, walkSync } from "../src/deno_ral/fs.ts";
-import { DOMParser, NodeList } from "../src/core/deno-dom.ts";
+import { DOMParser, Element, NodeList } from "../src/core/deno-dom.ts";
 import { assert } from "testing/asserts";
 import { basename, dirname, join, relative, resolve } from "../src/deno_ral/path.ts";
 import { parseXmlDocument } from "slimdom";
@@ -584,6 +584,63 @@ export const ensureFileRegexMatches = (
   return(verifyFileRegexMatches(regexChecker)(file, matchesUntyped, noMatchesUntyped));
 };
 
+// Use this function to Regex match text in CSS files linked from the HTML document
+export const ensureCssRegexMatches = (
+  file: string,
+  matchesUntyped: (string | RegExp)[],
+  noMatchesUntyped?: (string | RegExp)[],
+): Verify => {
+  const asRegexp = (m: string | RegExp) => {
+    if (typeof m === "string") {
+      return new RegExp(m, "m");
+    }
+    return m;
+  };
+  const matches = matchesUntyped.map(asRegexp);
+  const noMatches = noMatchesUntyped?.map(asRegexp);
+
+  return {
+    name: `Inspecting CSS files for Regex matches`,
+    verify: async (_output: ExecuteOutput[]) => {
+      // Parse the HTML file to find linked CSS files
+      const htmlContent = await Deno.readTextFile(file);
+      const doc = new DOMParser().parseFromString(htmlContent, "text/html")!;
+      const [dir] = dirAndStem(file);
+
+      // Find all stylesheet links and read their content
+      let combinedContent = "";
+      const links = doc.querySelectorAll('link[rel="stylesheet"]');
+      for (const link of links) {
+        const href = (link as Element).getAttribute("href");
+        if (href && !href.startsWith("http://") && !href.startsWith("https://")) {
+          const cssPath = join(dir, href);
+          try {
+            combinedContent += await Deno.readTextFile(cssPath) + "\n";
+          } catch {
+            // Skip files that don't exist (e.g., external URLs we couldn't parse)
+          }
+        }
+      }
+
+      matches.forEach((regex) => {
+        assert(
+          regex.test(combinedContent),
+          `Required CSS match ${String(regex)} is missing.`,
+        );
+      });
+
+      if (noMatches) {
+        noMatches.forEach((regex) => {
+          assert(
+            !regex.test(combinedContent),
+            `Illegal CSS match ${String(regex)} was found.`,
+          );
+        });
+      }
+    },
+  };
+};
+
 // Use this function to Regex match text in the intermediate kept file
 // FIXME: do this properly without resorting on file having keep-*
 export const verifyKeepFileRegexMatches = (