diff --git a/lib/internal/http.js b/lib/internal/http.js
index 999ade29ed07..0a6f5f2e6948 100644
--- a/lib/internal/http.js
+++ b/lib/internal/http.js
@@ -19,7 +19,8 @@ const {
 
 const { URL } = require('internal/url');
 const { Buffer } = require('buffer');
-const { isIPv4 } = require('internal/net');
+const { isIPv4, isIPv6 } = require('internal/net');
+const { canonicalizeIP } = internalBinding('cares_wrap');
 const { ERR_PROXY_INVALID_CONFIG } = require('internal/errors').codes;
 let utcCache;
 let utcHeaderCache;
@@ -75,6 +76,30 @@ function ipToInt(ip) {
   return result >>> 0;
 }
 
+function normalizeProxyHost(hostname) {
+  let host = hostname.toLowerCase();
+
+  if (host[0] === '[' && host[host.length - 1] === ']') {
+    host = host.slice(1, -1);
+  }
+
+  if (host.endsWith('.')) {
+    host = host.slice(0, -1);
+  }
+
+  if (isIPv6(host)) {
+    host = canonicalizeIP(host);
+    if (host.startsWith('::ffff:')) {
+      const ipv4 = host.slice(7);
+      if (isIPv4(ipv4)) {
+        host = ipv4;
+      }
+    }
+  }
+
+  return host;
+}
+
 // There are two factors in play when proxying the request:
 // 1. What the request protocol is, that is, whether users are sending it via
 //    http.request or https.request, or whether they are sending
@@ -137,7 +162,7 @@ class ProxyConfig {
       this.auth = `Basic ${Buffer.from(auth).toString('base64')}`;
     }
     if (noProxyList) {
-      this.bypassList = noProxyList.split(',').map((entry) => entry.trim().toLowerCase());
+      this.bypassList = noProxyList.split(',').map((entry) => normalizeProxyHost(entry.trim()));
     } else {
       this.bypassList = []; // No bypass list provided.
     }
@@ -159,7 +184,7 @@ class ProxyConfig {
       return true; // No bypass list, always use the proxy.
     }
 
-    const host = hostname.toLowerCase();
+    const host = normalizeProxyHost(hostname);
     const hostWithPort = port ? `${host}:${port}` : host;
 
     for (let i = 0; i < bypassList.length; i++) {
diff --git a/test/client-proxy/test-http-proxy-request-no-proxy-loopback.mjs b/test/client-proxy/test-http-proxy-request-no-proxy-loopback.mjs
new file mode 100644
index 000000000000..f8eb3967fe45
--- /dev/null
+++ b/test/client-proxy/test-http-proxy-request-no-proxy-loopback.mjs
@@ -0,0 +1,86 @@
+// This tests that NO_PROXY matches alternate loopback host spellings.
+
+import * as common from '../common/index.mjs';
+import assert from 'node:assert';
+import { once } from 'events';
+import http from 'node:http';
+import { runProxiedRequest } from '../common/proxy-server.js';
+
+if (!common.hasIPv6) {
+  common.skip('missing IPv6 support');
+}
+
+const server4 = http.createServer(common.mustCall((req, res) => {
+  res.writeHead(200, { 'Content-Type': 'text/plain' });
+  res.end('Hello World\n');
+}, 2));
+server4.listen(0, '127.0.0.1');
+await once(server4, 'listening');
+
+const server6 = http.createServer(common.mustCall((req, res) => {
+  res.writeHead(200, { 'Content-Type': 'text/plain' });
+  res.end('Hello World\n');
+}, 1));
+server6.listen(0, '::1');
+await once(server6, 'listening');
+
+// Start a proxy server that should NOT be used.
+const proxy = http.createServer();
+proxy.on('request', common.mustNotCall());
+proxy.on('connect', common.mustNotCall());
+proxy.listen(0);
+await once(proxy, 'listening');
+
+// A trailing dot in a DNS name should match the dotless NO_PROXY entry.
+{
+  const { code, signal, stderr, stdout } = await runProxiedRequest({
+    NODE_USE_ENV_PROXY: 1,
+    REQUEST_URL: `http://localhost.:${server4.address().port}/test`,
+    HTTP_PROXY: `http://localhost:${proxy.address().port}`,
+    NO_PROXY: 'localhost',
+    RESOLVE_TO_LOCALHOST: 'localhost.',
+  });
+
+  assert.match(stdout, /Status Code: 200/);
+  assert.match(stdout, /Hello World/);
+  assert.match(stdout, /Resolving lookup for localhost\./);
+  assert.strictEqual(stderr.trim(), '');
+  assert.strictEqual(code, 0);
+  assert.strictEqual(signal, null);
+}
+
+// Bracketed IPv6 URL hosts should match unbracketed NO_PROXY entries.
+{
+  const { code, signal, stderr, stdout } = await runProxiedRequest({
+    NODE_USE_ENV_PROXY: 1,
+    REQUEST_URL: `http://[::1]:${server6.address().port}/test`,
+    HTTP_PROXY: `http://localhost:${proxy.address().port}`,
+    NO_PROXY: '::1',
+  });
+
+  assert.match(stdout, /Status Code: 200/);
+  assert.match(stdout, /Hello World/);
+  assert.strictEqual(stderr.trim(), '');
+  assert.strictEqual(code, 0);
+  assert.strictEqual(signal, null);
+}
+
+// IPv4-mapped IPv6 loopback should match its IPv4 NO_PROXY entry.
+{
+  const { code, signal, stderr, stdout } = await runProxiedRequest({
+    NODE_USE_ENV_PROXY: 1,
+    REQUEST_URL: `http://[::ffff:7f00:1]:${server4.address().port}/test`,
+    HTTP_PROXY: `http://localhost:${proxy.address().port}`,
+    NO_PROXY: 'localhost,127.0.0.1,::1',
+  });
+
+  assert.match(stdout, /Status Code: 200/);
+  assert.match(stdout, /Hello World/);
+  assert.strictEqual(stderr.trim(), '');
+  assert.strictEqual(code, 0);
+  assert.strictEqual(signal, null);
+}
+
+proxy.close();
+server6.close();
+server4.close();