Kassen has had small parts in television films and TV series such as Another World in 1994, Cybill in 1997, and Third Watch 1999. In 2006, he produced the television movie Bernard and Doris with Susan Sarandon and Ralph Fiennes, which earned him, along with the other producers, nominations for a Golden Globe and Primetime Emmy Award for Best Television Film.
In 2011, he appeared in the drama film Puncture based off the true story of Michael David Weiss played by Chris Evans where Kassen played Weiss's law partner and best friend Paul Danziger. Kassen also directed and produced the film with his brother Adam Kassen.
It was announced in December 2013 that Kassen would star in the upcoming indie film Alone where he will play a 35-year-old veteran battling PTSD alongside Sophie Turner and Ray Liotta.