American screenwriter Musson wrote the script for the video game The Golden Compass to launch his career.

He contributed to the 2009 documentary film See What I'm Saying: The Deaf Entertainers Documentary as a writer as well. In November 2012, he was brought on to create the script for Jeremiah Harm. He agreed to write the script for the fantasy movie Iron Sky: The Coming Race in 2014.

Along with series creator Malcolm Spellman, he co-wrote the "Truth" episode of The Falcon and the Winter Soldier for the Marvel Cinematic Universe in 2021.

He co-wrote the MCU feature film Captain America: Brave New World (2025) with Spellman and director Julius Onah, which has brought him notoriety.