In 1989, after a few years of drawing television and toy tie-ins, he illustrated Ennis's debut, the political series Troubled Souls, in Crisis, as well as its sequel, the farce For a Few Troubles More. He later illustrated the series Carla Allison in Deadline.
He broke into American comics in 1993, drawing Ennis's run on DC Comics's The Demon, followed by its spin-off, Hitman, from 1996 to 2001, on which McCrea developed a versatile drawing style equally at home with goofy humour, action, and subtle characterisation. Hitman issue 34 won the Eisner Award for Best Single Issue in 1999. His wilder, more exaggerated cartooning found an outlet with Dicks, a mini-series spinning off from For a Few Troubles More into more outrageous dialect, sexual and toilet humour, published by Caliber in 1997, with a sequel, Dicks II, from Avatar in 2002.
On 9 April 2011, McCrea was one of 62 comics creators who appeared at the IGN stage at the Kapow! convention in London to set two Guinness World Records, the Fastest Production of a Comic Book, and Most Contributors to a Comic Book.[3][4]
In 2012, he started work on the Mars Attacks! 50th anniversary relaunch of the ongoing comic, written by John Layman and published by IDW. He also contributed 15 new cards to the Topps MA! Heritage set and exclusive variants for the set.
While pencilling and inking the MA! comic, he has also found time to pencil and ink issue 49.1 of Deadpool for Marvel, Warpaint (written by Phil Hester) for UK based Strip Magazine and Progenitor (also written by Hester) for David Lloyd's bold new online only publishing adventure Aces Weekly.
He returned to DC briefly in 2013 through their Vertigo imprint for an 8 pager (written by Neil Kleid) for their one shot Ghosts. He returned again, this time to mainline DC Comics, for miniseries Section 8, based on supporting characters of Hitman. Section 8 also marks his reunion with Hitman writer Garth Ennis and the team's return to the series.