How do I make a flowchart using markdown on my github blog

Update Feb. 2022: the Mermaid support is official (for Gist too):

Alternative Links 17/02/2020:

graph TD;
    A-->B;
    A-->C;
    B-->D;
    C-->D;

There is also an entry in the GitHub Docs

Working with Knut Sveidqvist and also the wider community at CommonMark, we’ve rolled out a change that will allow you to create graphs inline using Mermaid syntax, for example:

---

Update Sept. 2021: from GitHub tweet:

Need to add some ASCII art flow diagrams to your README or code comments?

YES → https://asciiflow.com (งツ)ว

This is not "markdown" per se, using "extended ASCII", but it can do the job.

---

Original answer 2016: The GitHub Flavored Markdown (GFM) alone does not support flowcharts (as opposed of other markdown like mermaid). You can confirm it in this GFM editor.

You would be better served by using some JavaScript library to display flowcharts.

As commented below by Jeremiah England, there is:

• a github/markup issue 533, with a possible workaround

• a feature request, which also includes workarounds:

  • a Chrome extension
  • a GitHub Action