"Recruit", a 2005 episode of the Superman prequel series Smallville, on which Johns' studio mate Jeph Loeb was a writer-producer, featured a villain by the name of Geoff Johns.
In 2008, Johns wrote "Legion", the eleventh episode of the eighth season, in which he introduced the three core members of the Legion of Super-Heroes.
At the 2009 San Diego Comic-Con, he announced that he was writing another Smallville episode, titled "Society," based on the Justice Society of America.
The success of his first episode and the ambitious nature of his follow-up episode enabled the producers to transform it into a two-part story, which subsequently aired as a feature-length episode titled "Absolute Justice".
Johns and David S. Goyer co-wrote the pilot for the Spike TV drama Blade, which premiered in June 2006. Johns served as one of the writing staff on the television show.
Later that year, Johns teamed up with Matthew Senreich of Robot Chicken fame to write the screenplay for a holiday family-friendly movie titled Naughty or Nice for Dimension Films. Johns and Senreich are billed as directors of the movie, with actor/producer Seth Green set to provide a lead voice as well as serving as voice director on the film. This association led to Johns contributing material to the fourth season of Robot Chicken.
In 2012, Johns joined The CW's Green Arrow origin series Arrow, as a writer. He first contributed to the first-season episode "Muse of Fire," which served as the introduction of The Huntress, the teleplay for which he co-wrote with executive producer Marc Guggenheim from a story by co-creator Andrew Kreisberg. Later in the season, Johns wrote the sixteenth episode, "Dead to Rights". The episode was directed by frequent Johns' collaborator Glen Winter.
On July 30, 2013, it was announced at the summer TCA tour that Johns and Arrow co-creators Kreisberg and Greg Berlanti would be introducing Barry Allen in the second season of the show, with the potential of a spin-off for the character with the 20th episode acting as a backdoor pilot. CW executives were so pleased with the handling of the character that they forwent the backdoor pilot, in favor of a full-fledged version.
In May 2014, The Flash was picked up to series, to premiere later that year. Johns serves as co-developer and executive producer. He co-wrote, with Kai Yu Wu, the episodes "Going Rogue", which introduces the villain Leonard Snart/Captain Cold to the series, and "Revenge of the Rogues", which brought the rogue Heat Wave to the series fully after being introduced off screen in "Going Rogue".
As of July 2015, Johns is collaborating with Reginald Hudlin and Denys Cowan on a live-action digital Static series from DC and Warner Bros. Blue Ribbon division.
Kreisberg, a producer on the TV series Supergirl, credits Johns with the idea that Hank Henshaw was really Martian Manhunter during production of that series' pilot in 2015.
In July 2018, Johns announced that he would be writing and executive-producing a DC Universe television series about Courtney Whitmore, a character that he created, titled Stargirl. The series premiered in May 2020.
In April 2020, it was reported that Johns is to produce a series based on Green Lantern for HBO Max.