Carol Alt, the third of four children, was born in Flushing, Queens, New York, to Muriel and Anthony Alt. She was raised in East Williston, New York, and she attended The Wheatley School and Hofstra University.

Alt's first big break in modeling was in 1980, when she was featured on the cover of Harper's Bazaar magazine, but she gained real fame in 1982 when she was featured on the cover of the Sports Illustrated Swimsuit Issue. During the 1980s she appeared on over 500 magazine covers, becoming one the most famous models of her era. Alt was referred to as "The Face" by Life Magazine. During the height of her popularity, she was the face of ad campaigns for Diet Pepsi, General Motors, Cover Girl Cosmetics, Noxema, Hanes and numerous others. She was the first model to produce her own posters and calendars. She was also the spokesmodel for the international cosmetics brand Lancôme in Europe, before being replaced by Isabella Rossellini As the eighties were winding down, Alt very publicly abandoned the fashion industry in favor of acting, which she said was her passion.

Since 1986 she has been in a variety of movies. Most were Italian, but one of her recent starring roles was in the Canadian movie Snakehead Terror. She played "Karen Oldham" in the TV adaptation of Peter Benchley's "Amazon" (1999). Her TV guest appearances include a 1996 episode of Wings were she plays a stripper and a voice role in the "Peggy's Pageant Fever" episode of King of the Hill, first broadcast November 10, 1998.

She has returned to her roots and taken on a number of model/spokesperson projects of late, including becoming a consultant with the "Le Mirador" skin-care line and appearing on late night TV infomercials. Alt has written two best-selling books, promoting her own raw food diet plans. She has been the cover girl for travelgirl magazine both in 2004 and 2008.