According to Entertainment Weekly, Walsh has been cast as the mother of protagonist Charlie, the so-called 'wallflower' who will be played by Percy Jackson & the Olympians: The Lighting Thief star Logan Lerman.
Walsh joins a growing cast list which also includes Harry Potter actress Emma Watson, The Vampire Diaries star Nina Nobrev, and Role Models actor Paul Rudd.
The book's author Stephen Chbosky will direct the adaptation from his own screenplay.
The Perks of Being a Wallflower is due to begin production in Pittsburgh later this month.
Walsh recently confessed that she feels "like a loser" for not having children.