In July 2008, he starred opposite Jennifer Westfeldt in the premiere of the play Finks, written by Joe Gilford and directed by Charlie Stratton for New York Stage and Film. Radnor made his directorial debut with the film Happythankyoumoreplease, where he was both the writer and star of the 2010 comedy-drama. His second directorial effort, Liberal Arts, starring himself and Elizabeth Olsen, premiered at the Sundance Film Festival on January 22, 2012. Radnor appeared in the Broadway production of Disgraced, which opened October 23, 2014 at the Lyceum Theatre. He is set to direct the sci-fi thriller film The Leaves. Radnor is currently starring in the Amazon Prime series, Hunters, as Lonny Flash.
In 2008, Radnor told the Los Angeles Times, "I do Transcendental Meditation, and part of the reason I chose my house is that I thought it would be a great place to meditate."