Sullivan began writing at the age of ten. Over a span of fifteen years, he wrote thirteen novels, but never made any serious attempts at publishing them. When he finally decided to seek publication, it was to produce a series of books that he wrote for his dyslexic daughter. His first published work, The Crown Conspiracy, was released in October 2008.

The Riyria Revelations is a six-book epic fantasy series. All the books were written before the first one was released. It abandons the recent trends in fantasy toward the lengthy, gritty, and dark, and brings the genre back to its roots and traditional elements. The series is centered around two thieves, Royce Melborne and Hadrian Blackwater and contains adventure, humor, and twisting plots. The two are reminiscent of buddy cop movies but set in a fantasy setting. Sullivan style has been compared to David Eddings and early Raymond E. Feist.

In addition to writing, Sullivan received a scholarship to attend the Center for Creative Studies as an artist. He formed his own advertising agency in 1996 and ran it until 2005 when he closed it to write full time. Sullivan also created the cover art for the series The Riyria Revelations. Unlike the depictions of the main characters on the covers of many fantasy novels, Sullivan instead illustrates on the cover a scene from the book.

Aspirations Media was the first publisher to print Sullivan's work releasing The Crown Conspiracy in October 2008. They also had a contract to publish his second book Avempartha, but by April 2009 it was announced that economic conditions required them to cancel the release of the second volume in the series. AMI's first printing of The Crown Conspiracy sold out in December 2009.

Ridan Publishing released the first edition of Avempartha in April 2009 and obtained the rights to The Crown Conspiracy from AMI, producing a second edition of that book in January 2010. They have subsequently released Nyphron Rising and The Emerald Storm, the third and fourth volumes in the series. Ridan is planning to release all six books in the Riyria Revelations series.

In March, 2010 it was announceed that two publishers in the Czech Republic were bidding for translations rights for that region.