diff --git a/src/main/EpubFontEmbedder.js b/src/main/EpubFontEmbedder.js
new file mode 100644
index 0000000..deb2b29
--- /dev/null
+++ b/src/main/EpubFontEmbedder.js
@@ -0,0 +1,37 @@
+'use strict';
+
+const fs = require('fs');
+const path = require('path');
+const JSZip = require('jszip');
+
+function withEpubEmbedFontArgs(pandocArgs, ttfPath, _fontFamily) {
+  return [`--epub-embed-font=${ttfPath}`, ...pandocArgs];
+}
+
+async function embedEpubFont(epubPath, ttfPath, _fontFamily) {
+  if (!ttfPath || !fs.existsSync(ttfPath)) {
+    throw new Error(`EpubFontEmbedder: TTF not found at ${ttfPath}`);
+  }
+  const bytes = fs.readFileSync(epubPath);
+  const zip = await JSZip.loadAsync(bytes);
+  const ttfBytes = fs.readFileSync(ttfPath);
+  const fontName = path.basename(ttfPath);
+  zip.file(`OEBPS/${fontName}`, ttfBytes);
+  const opfPath = 'OEBPS/content.opf';
+  const opfFile = zip.file(opfPath);
+  if (!opfFile) {
+    fs.writeFileSync(epubPath, await zip.generateAsync({ type: 'nodebuffer' }));
+    return;
+  }
+  let opf = await opfFile.async('string');
+  const manifestEntry = `<item id="font-${path.basename(fontName, '.ttf')}" href="${fontName}" media-type="application/x-font-ttf"/>`;
+  if (!opf.includes('manifest')) {
+    opf = opf.replace('</package>', `<manifest>${manifestEntry}</manifest></package>`);
+  } else if (!opf.includes(fontName)) {
+    opf = opf.replace('</manifest>', `${manifestEntry}</manifest>`);
+  }
+  zip.file(opfPath, opf);
+  fs.writeFileSync(epubPath, await zip.generateAsync({ type: 'nodebuffer' }));
+}
+
+module.exports = { withEpubEmbedFontArgs, embedEpubFont };
diff --git a/tests/unit/main/monospace/EpubFontEmbedder.test.js b/tests/unit/main/monospace/EpubFontEmbedder.test.js
new file mode 100644
index 0000000..b5ee766
--- /dev/null
+++ b/tests/unit/main/monospace/EpubFontEmbedder.test.js
@@ -0,0 +1,53 @@
+const fs = require('fs');
+const path = require('path');
+const os = require('os');
+const JSZip = require('jszip');
+
+const { withEpubEmbedFontArgs, embedEpubFont } = require('../../../../src/main/EpubFontEmbedder');
+
+async function makeMinimalEpub(outPath) {
+  const zip = new JSZip();
+  zip.file(
+    'META-INF/container.xml',
+    '<container xmlns="urn:oasis:names:tc:opendocument:xmlns:container"><rootfiles><rootfile full-path="OEBPS/content.opf" media-type="application/oebps-package+xml"/></rootfiles></container>'
+  );
+  zip.file('OEBPS/content.opf', '<package xmlns="http://www.idpf.org/2007/opf"></package>');
+  fs.writeFileSync(outPath, await zip.generateAsync({ type: 'nodebuffer' }));
+}
+
+describe('EpubFontEmbedder', () => {
+  let tmpDir;
+  beforeEach(() => {
+    tmpDir = fs.mkdtempSync(path.join(os.tmpdir(), 'mono-epub-'));
+  });
+  afterEach(() => {
+    fs.rmSync(tmpDir, { recursive: true, force: true });
+  });
+
+  test('withEpubEmbedFontArgs prepends --epub-embed-font', () => {
+    const args = withEpubEmbedFontArgs(['-o', 'out.epub', 'in.md'], '/tmp/font.ttf', 'JetBrains Mono');
+    expect(args).toContain('--epub-embed-font=/tmp/font.ttf');
+    expect(args.indexOf('--epub-embed-font=/tmp/font.ttf')).toBeLessThan(args.indexOf('-o'));
+  });
+
+  test('embedEpubFont adds font to OEBPS and updates manifest', async () => {
+    const epub = path.join(tmpDir, 'book.epub');
+    const ttf = path.join(tmpDir, 'JetBrainsMono-Regular.ttf');
+    await makeMinimalEpub(epub);
+    fs.writeFileSync(ttf, Buffer.from([0x01, 0x00]));
+
+    await embedEpubFont(epub, ttf, 'JetBrains Mono');
+
+    const zip = await JSZip.loadAsync(fs.readFileSync(epub));
+    const fontFile = zip.file('OEBPS/JetBrainsMono-Regular.ttf');
+    expect(fontFile).toBeTruthy();
+    const opf = await zip.file('OEBPS/content.opf').async('string');
+    expect(opf).toContain('JetBrainsMono-Regular.ttf');
+  });
+
+  test('embedEpubFont rejects missing TTF', async () => {
+    const epub = path.join(tmpDir, 'book.epub');
+    await makeMinimalEpub(epub);
+    await expect(embedEpubFont(epub, '/nope.ttf', 'JetBrains Mono')).rejects.toThrow(/TTF/);
+  });
+});