Marz is known for his work on Silver Surfer and Green Lantern, as well as the DC vs. Marvel crossover and Batman/Aliens. He co-created Genis-Vell in Silver Surfer Annual #6 (1993). Marz worked on the CrossGen Comics series Scion, Mystic, Sojourn, and The Path. At Dark Horse Comics he created Samurai: Heaven and Earth and various Star Wars comics. He has written for Devil’s Due Publishing’s Aftermath line including Blade of Kumori. In 1995, he had a brief run on X-O Manowar for Valiant Comics. The following year, Marz wrote the DC/Marvel: All Access limited series which was an intercompany crossover between DC and Marvel characters.

While writing Green Lantern, Marz wrote the “Emerald Twilight” storyline, in which the character of Hal Jordan, stricken with grief, became a mass murderer, leading to the destruction of the Green Lantern Corps, and Kyle Rayner being chosen at random as the last Green Lantern.

Marz’s 2000s work includes a number of Top Cow Productions comic books, including Witchblade, which he wrote from issue #80 (Nov. 2004) to issue #150, plus a number of specials and crossover stories featuring the character, such as Witchblade/The Punisher in 2007 and Witchblade/Devi in 2008. His other Top Cow work includes Cyberforce #1–6 in 2006 and Cyberforce/X-Men in 2007.

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 to participate with chapters for the book.

Marz became an editor of three of Virgin Comics’ Shakti Line titles in 2007 and oversaw Devi, Ramayan 3392 A.D. and The Sadhu. He wrote the Beyond series, based on a story created by Deepak Chopra.

In 2008 Marz wrote Broken Trinity, which featured the characters Witchblade, The Darkness, and Angelus, as well as the tie-in series, Broken Trinity: Witchblade, Broken Trinity: Angelus (2008), and Broken Trinity: Aftermath (2009). He signed an exclusive contract with Top Cow, which saw him write three comics a month: two for Marc Silestri’s Top Cow universe, and a creator-owned project.

In 2011, Marz was the writer on Voodoo, which was part of DC Comics’ company-wide title relaunch, The New 52.

In 2020 Marz collaborated with Andy Lanning on the nine-issue DC Comics crossover storyline “Endless Winter”, which would debut that December.