How can I view Markdown text inside Visual Studio?

The accepted answer is five years old, and the respective extension supports only up to Visual Studio 2015. Today, for Visual Studio 2019 and below, I would recommend Markdown Editor by Mads Kristensen. It has over 400K installs, supports GitHub and other flavors, live preview window, automatic HTML file generation, and much more. Works with both file extensions .md and .mkd..

You can also use Visual Studio Code instead of Visual Studio, then you have excellent markdown support with live preview built-in. There is an extension Markdown Preview Github Styling. For even more functionality, another great extension is Markdown All In One.

Maybe you can use the extension Markdown Mode

http://visualstudiogallery.msdn.microsoft.com/0855e23e-4c4c-4c82-8b39-24ab5c5a7f79