Molly Shannon was born in Shaker Heights, Ohio. She was in a car crash at age 4 that killed her 34 year old mother, her 3 year old sister, and a 25 year old cousin.
Her mother, Peg Shannon, was a teacher, and her father, James F. Shannon, was a sales manager.
She graduated from St. Dominics School in Shaker Heights, Ohio and also graduated from NYU with a Bachelors of Fine Arts from NYU's Tisch School of the Arts. Molly struggled at the beginning of her career, appearing in small roles in films and TV shows, her major break came in February 1995, when she was hired as a player on Saturday Night Live to replace Janeane Garofalo. She was one of the few cast members that were kept on in Seasons 20-21.
She also played Emily Sanderson in A Night at the Roxbury in 1998 and Mary Katherine Gallagher in Superstar in 1999. She later appeared in the FOX series, Cracking Up, Marie Antoinette and guest-starred on Pushing Daisies and Scrubs. She left SNL in 2001.
She was recently cast as Brenda Castle as a recurring role on Glee.
Molly married artist, Fritz Chesnut, on May 29, 2004. They have two children: Stella, born in 2003 and Nolan, born in 2005.