He is known for his work on the TV series Daredevil, Hawaii Five-0, Law & Order: Special Victims Unit, Numbers and the films The Breed and Teenage Caveman.

[citation needed] They co-wrote the 2001 film The Breed, starring Adrian Paul, Bai Ling and Bokeem Woodbine, for Sony/Screen Gems and Starz.

The Gages co-wrote episodes of the TV shows Law & Order: Special Victims Unit and Numbers.

[18] Gage wrote the tie-in book Avengers: The Initiative, co-writing with Dan Slott beginning with issue #8, and eventually becoming the sole writer for the series with #20.

[20][21] That same year he wrote the first seven issues of The Man with No Name for Dynamite Entertainment, which stars the iconic Western character portrayed by Clint Eastwood.

[22] Later that year he wrote the creator-owned series Absolution for Avatar Press, which focuses on a superhero actions after he develops post-traumatic stress disorder and thus resorts to murdering supervillains.

[23] In 2010 Gage wrote the original graphic novel Area 10, a crime thriller about an emotionally disturbed New York police detective who, while on the case of a bizarre serial killer, begins to exhibit psychic abilities after his head is impaled by a screwdriver.

[1] In 2011 Gage was approached to write Angel & Faith, the canonical continuation of the adventures of Joss Whedon's Buffyverse characters, as part of Buffy The Vampire Slayer Season Nine.

[24] In July 2012 Gage published the original graphic novel Sunset, through Top Cow/Minotaur Press, a noir tale of an aged mob enforcer facing the demons of his violent past.

[25] As of 2012 Gage and his wife Ruth were working on the historical epic The Lion Of Rora for Oni Press.

[28] In the same year, Gage and Angel & Faith artist Rebekah Isaacs took over the Buffy The Vampire Slayer title, beginning with Season 10.

The series focuses on the character Violet, and an edition with all three issues was released on October 1, 2019, again by Dark Horse Comics.

Gage and Dan Slott are among the writers of the 2018 game Marvel's Spider-Man, developed by Insomniac Games[36] which sold 3.3 million copies in the first three days of release [37] and earned the writers a WGA Award nomination[38] as well as BAFTA[39] and SXSW[40] award nominations.