Shamos is a character actor. His most notable roles are Craig Kettleman on Better Call Saul, Johanes Karlsen in Nurse Jackie, and Ralph in the film Birdman or (The Unexpected Virtue of Ignorance). Shamos is also a stage actor, starring in productions including Steve Martin's Meteor Shower, Clybourne Park for which Shamos was nominated for a Tony Award, The Qualms, The Assembled Parties, Dinner with Friends, 100 Saints You Should Know, and Elling.