Yes that is what RedGard is for (I assume you are planning to tile over the top of it). It is a waterproof membrane, it stops any water that might make it through the cracks in the tile (or grout). It is not intended to stand up to the abuse of a normal shower wall or floor so it must be covered with tile.
From the company's website:
Rated for extra heavy duty service
Meets Uniform Plumbing Code specifications for use as a shower pan liner
I used RedGard to waterpoof behind my tiles in my tub surround. It was pretty easy to work with.