In 2003, Kirkman and Walker created Invincible for Image's new superhero line. The story surrounded the adolescent son of the world's most powerful superhero, who develops powers and starts his own superhero career. Walker later failed to meet the monthly title's deadlines and was replaced by Ryan Ottley. In 2005, Paramount Pictures announced it had bought the rights to produce an Invincible feature film, and hired Kirkman to write the screenplay.
Shortly after the launch of Invincible, Kirkman and Moore began The Walking Dead (2003). Moore, struggling to meet deadlines, was replaced by Charlie Adlard, beginning with issue #7. Moore continued to draw covers until issue 24 as well as the first four volumes of the trade paperbacks for the series.
At Image, Kirkman and artist Jason Howard created the ongoing series The Astounding Wolf-Man, launching it on May 5, 2007, as part of Free Comic Book Day. Kirkman edited the monthly series Brit, based on the character he created for the series of one-shots, illustrated by Moore and Cliff Rathburn. It ran 12 issues.
In late July 2008, Kirkman was made a partner at Image Comics, thereby ending his freelance association with Marvel. Nonetheless, later in 2009, he and Walker produced the five-issue miniseries The Destroyer vol. 4 for Marvel's MAXimprint.
In 2009, Kirkman and Marc Silvestri took over the 2009–2010 Pilot Season for Top Cow Comics. The 2009/2010 Pilot Season contains a series of five one-shot pilot comics that readers will be able to vote on which becomes an ongoing series. Each series is co-created by Silvestri who also provides cover art.
In 2010, he also began producing the television adaption of his comic book series The Walking Dead, the pilot of which was directed by Frank Darabont. Kirkman wrote the fourth episode, "Vatos".
On February 9, 2012, Tony Moore filed a lawsuit alleging that Kirkman, in 2005, had deceitfully engineered him into surrendering his rights to The Walking Dead comic book and eventual TV series in exchange for payments that never materialized. Kirkman said in a statement the following day that he and Moore "each had legal representation seven years ago and now he is violating the same contract he initiated and approved and he wants to misrepresent the fees he was paid and continues to be paid for the work he was hired to do." Kirkman in turn sued Moore. On September 24, 2012, the two released a joint statement saying they had reached a settlement "to everyone's mutual satisfaction."
Kirkman and his wife live in Kentucky. He named his son Peter Parker Kirkman after Spider-Man's civilian identity, Peter Parker.
^Per The Unofficial Handbook of Marvel Comics Creators, the earlier volumes star an unrelated character adapted from The Destroyer series of novels: The Destroyer (1989–1990), The Destroyer vol. 2 (1991) and The Destroyer vol. 3 (1991–1992)