Wacker got his start in comics creating a live comic-book themed show called Ka-Baam!!, which included improvisors such as Adam Felber, Paul Scheer, and Victor Varnado, and also folded in notable comic book artists and editors as guests, which led to an interview for a job at DC Comics. In 2000, Wacker was hired as an assistant editor where he worked on comics including JLA, JSA, and 52.
He was recruited by Marvel Comics in 2006 and held the position of senior editor, working primarily on the Spider-Man titles (including Brand New Day) and Guardians of the Galaxy franchises. In 2013, he relocated from Marvel Comics's New York headquarters to Marvel Animation in Los Angeles where he held the position of VP of Animation. Wacker is credited as co-executive producer on many of their animated series, including the Avengers Assemble and Guardians of the Galaxy series that aired on Disney XD. In 2017, he transferred to Marvel Television where he was a VP of Development where he produced Marvel's Hero Project, Marvel's 616, and Marvel's Behind the Mask. In 2020, Wacker transferred to Marvel Digital Media as VP Head of Content. In 2022, he was hired as editor-in-chief at 3W/3M Comics (Three Worlds/Three Moons) and left the following year to co-found the entertainment studio Stone Kite. In July 2026, Wacker was announced to be returning to Marvel Comics as its editor-in-chief, succeeding C. B. Cebulski.