From 1975–1978, Warner served as an editor and writer for the black-and-white Marvel imprint Curtis Magazines, where he worked primarily on Deadly Hands of Kung Fu, but also on Doc Savage, Marvel Preview, and Rampaging Hulk. For the latter series he created the characters Killer Shrike and the Modular Man. Separately, he co-created Ulysses Bloodstone. During his stint as a Marvel/Curtis editor, Warner hired Ralph Macchio, who has since gone on to a long-running career at Marvel.

In addition, Warner wrote most of the run of Marvel's Son of Satan, and in the late 1970s wrote Gold Key's Flash Gordon comic.

Warner lists as his influences Arthur Rackham, N.C. Wyeth, Gerry Anderson, Maxfield Parrish, Chuck Jones, Jay Ward, Ray Bradbury, and Jorge Luis Borges.

Warner is married to the former Beth Bleckley.