Marz is known for his work on Silver Surfer and Green Lantern, as well as the Marvel vs DC crossover and Batman/Aliens. He also worked on the CrossGen Comics series Scion, Mystic, Sojourn, and The Path. At Dark Horse Comics he created Heaven and Earth and various Star Wars comics. He has also done work for Devil's Due Publishing's Aftermath line, namely Blade of Kumori. In 1995, he had a brief run on XO-Manowar, for Valiant Comics.

While writing Green Lantern, Marz wrote the "Emerald Twilight" storyline, in which the character of Hal Jordan was turned into a mass murderer in order to make way for a new Green Lantern character, Kyle Rayner.

Marz's more recent works includes a number of Top Cow books including Witchblade and an upcoming Cyberforce relaunch. For DC Comics, he has written Ion, a 12 part comic book miniseries that followed the Kyle Rayner character after the One Year Later event, and Tales of the Sinestro Corps Presents: Parallax and Tales of the Sinestro Corps Presents: Ion, two one-shot tie-ins to the Green Lantern crossover, The Sinestro Corps War.

Marz wrote Moonstone Books' 2006 Annual featuring The Phantom, and was responsible for getting writers Chuck Dixon, Mike Bullock, Tony Bedard, and Rafael Nieves participate with chapters for the book. Marz has also signed on to write a short story with the character for one of Moonstone's upcoming Phantom prose collections.

In 2007 Virgin Comics announced that Marz would be joining as editor of three of their Shakti Line titles: Devi, Ramayan 3392 A.D. and The Sadhu. He also wrote the series Beyond, based on a story created by Deepak Chopra.

At Top Cow he is writing Broken Trinity, which features the characters Witchblade, The Darkness and Angelus. This led to the announcement at the 2008 Baltimore Comic-Con that he had signed an exclusive contract with Top Cow which will entail three comics a month - two "Top Cow Universe" titles and a creator-owned project.

Comics work includes:

• Beyond (with Edison George, Virgin Comics, 2008)
• Broken Trinity (with Stjepan Sejic, 3-issue mini-series, Top Cow, 2008, forthcoming)
• Dragon Prince (with Lee Moder, Top Cow, 2008)