GitHub Gist WordPress Plugin allows you to embed <a href="http://gist.github.com" rel="nofollow ugc">GitHub Gist</a> snippets with a [gist] tag, instead of copying and pasting HTML. For example, to embed the <a href="http://gist.github.com/447298.js?file=github_gist_wordpress_plugin_test.txt" rel="nofollow ugc">github_gist_wordpress_plugin_test.txt</a> file from <a href="http://gist.github.com/447298.js" rel="nofollow ugc">gist: 447298</a>, fill in the id and file attributes in the [gist] tag:
[gist id=447298 file=github_gist_wordpress_plugin_test.txt]
or
copy the embedding JavaScript code from GitHub and directly paste it in the body of the [gist] tag:
[gist]<code><script src="http://gist.github.com/447298.js?file=github_gist_wordpress_plugin_test.txt"></script></code>[/gist].
The [gist] tag also expands the content of the embedded Gist and wraps it with “<code><noscript><code><pre></code>” so that search engine spiders, users with javascript disabled and users reading your blog through RSS will still see your code in a blog entry.

GitHub Gist WordPress Plugin

GitHub Gist Wordpress Plugin allows you to embed GitHub Gist snippets with a [gist] tag, instead of copying and pasting HTML.

Andy Fragen

Colin Stewart

Use an Embed block and enter the URL for the Gist or the URL for a specific file within the Gist. If using the Classic Editor, place the URL on a line by itself. Not as a link.
Support for <code>wp_oembed_get()</code>.
No shortcodes.

GitHub Gist WordPress Plugin vs oEmbed Gists and Files