A source close to the show confirmed the Season 11 casting news to The Los Angeles Times, but it has yet to be announced officially.
Tamblyn, 30, is known for her work on the TV shows "Joan of Arcadia" and "General Hospital." She also co-starred in the "Sisterhood of the Traveling Pants" movies.
Sheen played Harper until he was fired at the end of Season 8 for his drug use, erratic behavior and insubordination to show creator Chuck Lorre.
The show's ninth season kicked off with Harper's funeral and the arrival of Ashton Kutcher's Walden Schmidt character.