Gross was attended St. John's University and did graduate studies at the University of Wisconsin-Superior. He intended to make a living as a fine artist, but was drawn into comics, first doing some work for Marvel and then following it up with his originally-self-published series Empire Lanes.

Comics work includes:

• The Books of Magic #4, 6-8, 18-19, 21-30, 39-41, 43-62, 64-75 (art and (from #51) script, with writer John Ney Rieber, ongoing series Vertigo, August 1994 - August 2000)
• Lucifer #5-8, 10-13, 15-19, 21-23, 25-27, 29-32, 34-40, 42-44, 46-49, 51-54, 56-57, 59-61, 63-65, 67-69, 71-72, 74-75 (with writer Mike Carey, ongoing series, Vertigo, October 2000 - August 2006) collected as:
• Volume 2 Children and Monsters (collects Lucifer #5—13, Vertigo, 2001, ISBN 1840233915)
• Volume 3 A Dalliance with the Damned (collects Lucifer #14—20, Vertigo, 2002, ISBN 1840234709)
• Volume 4 The Divine Comedy (collects Lucifer #21—28, Vertigo, 2003, ISBN 1840236930)
• Volume 5 Inferno (collects Lucifer #29—35, Vertigo, 2004, ISBN 1-4012-0210-1)
• Volume 6 Mansions of the Silence (collects Lucifer #36—41, Vertigo, 2004, ISBN 1-4012-0249-7)
• Volume 7 Exodus (collects Lucifer' #42—44 & #46—49, Vertigo, 2005, ISBN 1-4012-0491-0)
• Volume 8 The Wolf Beneath the Tree (collects Lucifer #45 & #50—54, Vertigo, 2005, ISBN 1-4012-0502-X)
• Volume 9 Crux (collects Lucifer #55—61, Vertigo, 2006, ISBN 1-4012-1005-8)
• Volume 10 Morningstar (collects Lucifer #62—69, Vertigo, 2006, ISBN 1-4012-1006-6)
• Volume 11 Evensong (collects Lucifer #70—75, Vertigo, 2007, ISBN 1-4012-1200-X)

• Chosen (with writer Mark Millar, 3-issue mini-series, Dark Horse Comics, 2004, tpb, Image Comics, 72 pages, December 2008, ISBN 160706006X)
• The Unwritten #1- (with Mike Carey, ongoing series, Vertigo, July 2009-ongoing)