Rannells, who was seen last season in the now-canceled NBC comedy "The New Normal," is scheduled to become a series regular should "Girls" be picked up for a fourth season.
"Girls" will return for its third season on the cable network Jan. 12, 2014, at 9 PM ET; check local listings. In addition to Dunham, the cast also features Jemima Kirke, Allison Williams, Zosia Mamet, Adam Driver and Alex Karpovsky.
Rannells' previous Broadway outings include leading roles in Jersey Boys and Hairspray.