The 50-year-old actor will guest star in a recurring role on the fifth season of the Showtime series. Mulroney will portray Sean Pierce, an ex-bad boy and recovering addict who becomes Fiona's (Emmy Rossum) new love interest and manager at Patsy's Pies.
The program co-stars William H. Macy as Frank Gallagher, a single father to six children. Fiona is his eldest daughter and sister to Phillip (Jeremy Allen White), Ian (Cameron Monaghan), Carl (Ethan Cutkosky), Liam (Brennan Kane Johnson and Blake Alexander Johnson) and Debbie (Emma Kenney). The show is a comedy drama that depicts the day-to-day life of the dysfunctional family.
Mulroney most recently appeared in August: Osage County, and has guest starred on television series Crisis, New Girl and Enlightened. The fifth season of Shameless premieres on Showtime in 2015.