Rathburn got some early work at DC Comics but became best known for providing the grey colouring for Robert Kirkman's long-running series The Walking Dead at Image Comics. Also at Image he did the artwork on Kirkman's Reaper and Brit one-shots before going on to provide the complete art for the first six issues of Brit, his first ongoing series. In between he also worked at Marvel Comics.

Recent work involves inking the pencils of Simon Coleby and Tony Harris on The Authority and War Heroes, respectively. In 2011 Rathburn was awarded the S.P.A.M.I. Award (Favorite Small Press and Mainstream-Independent 2010 cover-dated interior comic book ink work over another pencil artist (Non-Marvel or DC work)) by the Inkwell Awards.