Ephraim performed in shows at the Bucks County Playhouse as a child and as a teenager, and in professional productions at the Prince Music Theater and Arden Theatre Company in Philadelphia. In 2008 she graduated from Princeton University, where she was a member of the Triangle Club. She performed in and choreographed various shows for Princeton University Players and Theatre Intime.
On television, Ephraim has had roles in episodes of Royal Pains, Law & Order and the TV movie Hench at Home.
She made her Broadway debut in 2002 as Little Red Riding Hood in the Broadway revival of Into the Woods, receiving a Drama League Award nomination. Ephraim was later seen as Bielke in the 2004 Broadway revival of Fiddler on the Roof. Off-Broadway, she played Rachel Stein in End Days at the Ensemble Studio Theatre in 2009. In 2008 she was Olive in The 25th Annual Putnam County Spelling Bee at the Barrington Stage Company and at the North Shore Music Theatre. In 2010 she played Anne Frank in The Diary of Anne Frank at the Westport Country Playhouse.
Ephraim, who has a menagerie of pets, currently lives in the Los Angeles area.
Molly Ephraim Facts