[2] After his work in the military and at Ringling College of Art and Design, Bagley continued trying to break into the comic industry.

While working a construction job, he suffered a severe injury to his leg while using a handsaw that required 132 stitches.

[7] The following year, Marvel launched a new series based on these heroes and assigned Bagley and writer Fabian Nicieza to the title.

He and David Michelinie introduced the Carnage character in The Amazing Spider-Man #361 (April 1992)[9] and produced the Venom: Lethal Protector limited series in 1993.

Bagley's artwork was used extensively for licensed material, appearing on everything from plates and cups to credit cards and even video games such The Amazing Spider-Man: Lethal Foes released exclusively in Japan.

[13] In 1997, Bagley collaborated with writer Kurt Busiek on a new team of superheroes, the Thunderbolts, a group of super-villains disguised as super-heroes, with the final page of the first issue of the series revealing that the Thunderbolts were actually the Masters of Evil, a surprise twist carefully guarded by Marvel.

[18] His first assignment as a DC exclusive, the Trinity weekly series written by Kurt Busiek featured Superman, Batman, and Wonder Woman.

He reunited with writer Brian Michael Bendis and drew the "Death of Spider-Man" arc in issues #156–160.

Bagley and Bendis teamed for a creator-owned series, Brilliant, which was published through Marvel's Icon Comics Imprint.

[30] In late 2017, Bagley made a return to Venom with issue #155, "Lethal Protector", written by Mike Costa.

[5] According to Bagley, drawing crowd scenes are his "weak point", because he becomes worn out on them, and finds them difficult to render in a timely fashion.