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.

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.

Kirkman announced in 2007 that he and artist Rob Liefeld would team on a revival of Killraven for Marvel Comics. Kirkman that year also said he and Todd McFarlane would collaborate on Haunt for Image Comics.

Robert Kirkman’s first comic book work was the 2000 superhero parody Battle Pope, which he co-created with artist Tony Moore, self-published under the Funk-O-Tron label, and was adapted into a season of 8 animated webisodes that appeared on Spike TV’s website in 2008. Later, while pitching a new series, Science Dog, Kirkman and artist Cory Walker were hired to do a SuperPatriot miniseries for Image Comics. While working on that book, Kirkman and E. J. Su created the 2002 Image series Tech Jacket, which ran six issues, and the one-shot title, Cloudfall.

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 MAX imprint.

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 has written or co-written seven episodes of the series. Kirkman also created and serves as an executive producer on the show’s companion series, Fear the Walking Dead.

In July 2010, Kirkman announced he would launch and run a new Image Comics imprint called Skybound Entertainment.

Shortly after the launch of Invincible, Kirkman and Moore began The Walking Dead (2003). Kirkman said in 2012 that Image had balked at publishing a comics series featuring what it felt was simply another zombie story, prompting him to say the zombies were part of an alien plot—a notion he had no intention of using except as a means of selling the project. Artist Charlie Adlard replaced Tony Moore 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.

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 made an appearance in a 2012 episode of Adult Swim’s Robot Chicken as himself where he tries to tell The Nerd and Daniel a hint, but gets eaten by the zombies.

In November 2013, Cinemax purchased a TV pilot based on Kirkman and artist Paul Azaceta’s then-upcoming six-issue exorcism comics miniseries, Outcast. The first issue of the comic was released in June 2014 to positive reviews.

Kirkman was a producer of the science fiction thriller Air, which starred The Walking Dead’s Norman Reedus, and Djimon Hounsou. The movie was released in 2015. It was the first feature film to be produced by Skybound Entertainment.

Kirkman’s latest television project known as Five Year will be a joint venture between Skybound and Viki.com. It will be filmed for TV in Korea and available everywhere on Viki.com. The pre-apocalyptic story centres on a family dealing with an impending meteor strike. It was picked up for an initial 1 season run of 16 episodes with a plan for 5 seasons. Filming begins in late 2016.

In 2020, he is granted a special award (“Fauve d’honneur”) at the Angoulême International Comics Festival for his overall achievement.