He is best known for co-writing the screenplays for the films Doom (2005), The Expendables (2010), Zombieland: Double Tap (2019), Wonder Woman 1984 (2020), Mortal Kombat, Shang-Chi and the Legend of the Ten Rings (both 2021), and Spider-Man: Across the Spider-Verse (2023).
[9] 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.
[11] In 2010, Legendary Pictures hired Callaham to write the first draft for Godzilla, for which he received a story credit.
In April 2020, Callaham was announced as the writer of Walt Disney Pictures' live-action remake of Hercules.
[20] In January 2022, Callaham was announced to have written the latest draft of screenplay of the Masters of the Universe reboot for Netflix, along with Aaron and Adam Nee.
[21] On May 1, 2024 it was confirmed that the Masters of the Universe film would now be released through Amazon MGM Studios and Mattel Films and would be directed by Travis Knight with a screenplay written by Chris Butler that would be based on the initial draft written by Callaham and Aaron and Adam Nee.
[23] 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.