Johns was born in Detroit and studied media arts, screenwriting, and film at Michigan State University. After moving to Los Angeles, he became an assistant to Richard Donner, director of Superman: The Movie. He and his mentor Donner later co-wrote Superman: Last Son featuring the return of General Zod.
Johns has written for various other media, including episodes of Smallville, Arrow and Adult Swim's Robot Chicken, for which he was nominated along with his co-writers for an Emmy. He is the Chief Creative Officer of DC Entertainment and resides in Los Angeles, California.