Is it possible to present Markdown rendered in an Emacs buffer using Emacs\' own buffer text formatting capabilities? Emacs in graphical environments has rich text presentation
If it is only about the rendering, go with Bozhidar's suggestion and do a Markdown to HTML conversion, then display the HTML in a W3 buffer. markdown-mode has code to call the external Markdown command with a few goodies.
But if you really want to do everything within Emacs Lisp, you'll have to write a Markdown parser first.