After reading an article in Penthouse magazine focusing on the lifestyle of Hollywood TV writers, Callaham and a friend moved to Los Angeles with plans to write comedies together. They sent query letters to multiple agencies but never received responses. Callaham worked at Creative Artists Agencyfor a while, sometimes submitting his material secretly for coverage. In 2003, Callaham wrote the film adaptation to the video gameDoom and submitted it in the summer of 2005. Around that time, Callaham wrote Barrow for Warner Bros., a mercenary-inspired action script which later became The Expendables. Callaham was credited for story and characters after Sylvester Stallone used Callaham's Barrow script as a "starting point" for The Expendables. In 2010, Legendary Pictures hired Callaham to write the first draft for Godzilla, for which he received a story credit. In 2014, Callaham completed a production rewrite for Ant-Man, and in 2019, he co-wrote the Zombieland sequel, ', for Sony. He has also worked on the yet-unproduced Jackpot for Focus Features and America: The Motion Picture for Netflix. In October 2016, Universal Pictures hired Callaham to rewrite The Wolf Man for their Dark Universe. In September 2017, Patty Jenkins hired Callaham to write the script for Wonder Woman 1984 with her and Geoff Johns. In December 2018, Marvel Studios hired Callaham to write the screenplay for a film based on Shang-Chi. Sony Pictures Animation hired Callaham to write a sequel to '. In April 2020, Callaham was announced as the writer of Walt Disney Pictures' live-action remake of Hercules.
Lawsuit
In late 2013, Nu Image and Millennium Films filed a lawsuit against Callaham and the Writers Guild of America West for fraud, unjust enrichment and declaratory relief over a "flawed and misinformed" Guild arbitration that gave Callaham undeserved writing credit for The Expendables and The Expendables 2. The plaintiffs have accused Callaham for intentionally withholding emails and other correspondences from the WGA screen writing credit arbitration panel in 2009 that according to the plaintiffs reveal how very little Callaham was involved with The Expendables and demand reimbursements from Callaham for any payments made to him for his fraud credit in the two films. When Sylvester Stallone was developing the script for The Expendables, Callaham claimed that Stallone used his script, Barrow, as the source for The Expendables. A WGA arbitration was ignited in which Callaham won and additionally earned $102,250 in bonus payments. However, the plaintiffs have uncovered emails from Callaham admitting that his script is nothing like Stallone's script.
