Beverly Marsh was born in 1947. She is the daughter of Alvin and Elfrida Marsh. Her mother's presence in her life differs among the three continuities.

Beverly is a classmate of Ben Hanscom, who harbors a secret crush on her. Ben writes her an anonymous love poem which states, "your hair is winter fire, January embers, my heart burns there too." Beverly is led to believe that the poem was written by Bill Denbrough, who grows up to be a professional writer.

Beverly eventually joins "The Losers Club" and befriends Eddie Kaspbrak, Richie Tozier, Mike Hanlon and Stanley Uris. Beverly has her first encounter with Pennywise in her bathroom when she hears voices coming from her sink chanting "We All Float Down Here". A balloon-like construct begins growing from her sink and bursts, covering her bathroom with blood. Beverly's screams attract the attention of her father, who cannot see the blood. She confides in The Losers Club, who can all see the blood and help her clean the bathroom.