Biel was born on March 7, 1982, in Ely, MN, then raised in Boulder, CO. She was first discovered at the 1994 IMTA Los Angeles Convention, which earned her a scholarship to Diane Hardin's Young Actors Space in Los Angeles. Teen print modeling followed, and in 1996, Biel began her run as Mary Camden on the Aaron Spelling-produced 7th Heaven. Shortly thereafter, she was cast as Peter Fonda's granddaughter in Victor Nunez's rich character study, Ulee's Gold (1997), and as Jonathan Taylor Thomas' love interest in I'll Be Home for Christmas (1998).

But Biel grew tired of playing a good girl on television and tried to force the producers to fire her from 7th Heaven, claiming her pristine image was a factor that kept her from landing the role that went to Thora Birch in American Beauty (1999). When the producers would not release her from her contract, she posed on the cover of the March 2000 Gear under the headline "Fallen Angel." The images inside featured her sprawled topless on a bed and against a bathroom mirror, her hands providing insufficient cover in a manner that pushed even Gear's lax standards for showing skin. The issue become one of Gear's most popular ever, with terrific resale value on Ebay, and got Biel canned from the show.