Fawkes started his career in comics with books such as Possession and One Soul at Oni Press, and as an artist on the book Mnemovore for Vertigo Comics. He first broke out into DC Comics in 2013 writing Batgirl for two issues after then writer Gail Simone was let go from the title, then rehired after backlash. He was then moved onto Justice League Dark #17-21 with writer/artist and fellow friend Jeff Lemire. He and Lemire would then collaborate again, this time as co-writers on the book Constantine, until Lemire left after Issue 4, leaving Fawkes as the sole writer of the book. He would also then take another title Trinity of Sin: Pandora. In 2014, he was one of the many writers announced to be working on the weekly series Batman Eternal.
In August of 2014, he released The People Inside, the spiritual successor to his graphic novel One Soul.
In October 2014, he and Ben Templesmith launched another title called Gotham by Midnight, spinning off from Batman Eternal. In November 2014, he wrote and drew a new ongoing book called Intersect at Image Comics.
In January 2015, he and Charles Soule launched a weekly series together at Marvel Comics titled Wolverines, a continuation from the Death of Wolverine storyline written by Soule. Prior to joining the title, he wrote a Daken story in Death of Wolverine: The Logan Legacy.