In 2011, Knapp made his film debut as Breen in the science-fiction adventure film
Super 8. He played Denny in the horror thriller film
No One Lives (2012). On television, Knapp appeared in a
2013 episode of the television series
Bones. Other film roles include the character Jonah Breck in the science fiction thriller
The Signal (2014), Jackson in the drama ''
You're Not You (2014), Kenan Boyle in the crime thriller Run All Night (2015), and Jon Jon in the boxing drama Southpaw'' (2015). In 2016, Knapp played the best friend of
Chris Pine's character in the disaster drama film
The Finest Hours. He then played the villain Blue Face in the mystery thriller
The Nice Guys, as well as violent Crack in the war film ''
Billy Lynn's Long Halftime Walk''. Knapp appeared in the
Netflix war drama film
Sand Castle (2017), and in a co-starring role in the Netflix series
Seven Seconds (2018). Knapp appeared as the main villain, opposite
Bruce Willis, in
Eli Roth's
remake of
Death Wish. He also played the main antagonist in
Measure of a Man. In 2024, Knapp portrayed Drew Franklin in season 7 of
SEAL Team. In 2025, Knapp had a major role in season three of
Tulsa King on Paramount. ==Filmography==