Biel was born to Jonathan Edward Biel and Kimberly Conroe. Biel, who has a younger brother, Justin, grew up in Boulder, Colorado, where her family had moved when she was very young. She initially trained to become a vocalist with the hope of performing in musical theater and appeared in several musicals at an early age including The Sound of Music, Annie, Beauty and the Beast, and Anything Goes.

It wasn't until she attended the International Modeling & Talent Association Convention in Los Angeles in 1994 when her career started to take off as a fashion model. However, her big break came when at 14 years old she landed the role of Mary Camden on the WB TV Series 7th Heaven. The family drama from Aaron Spelling and Brenda Hampton became the most popular (and remains the longest running) series on the fledgling network. Jessica's film career also began at age 15 when she played alongside Peter Fonda in his Golden Globe winning performance in Ulee's Gold (1997). Aside from acting, Jessica became a spokesmodel for L'Oreal cosmetics in 2002.

In 2000, Biel posed topless in a layout of Gear magazine. It was controversial because she was only 17 at the time of the shoot. Her frustration and fear about being typecast was one of the reasons that led to her decision. She blamed her saintly image on 7th Heaven for limiting her film career, including losing a lead role in American Beauty which eventually went to Thora Birch. Jessica also hoped that by posing she would get out of her 7th Heaven contract, which she accomplished. She later said she regretted posing for the magazine and regards it as a learning experience. Jessica returned to 7th Heaven full time for the 2001-2002 season and then focused the attention on her movie career and has made minimal TV appearances since then.

After her departure from 7th Heaven she accepted projects mainly geared to teens and young adults including Summer Catch (2001), The Rules of Attraction (2002) and Texas Chainsaw Massacre (2003). The movies were met with mild reaction from the box office and panned by many critics. However due to her acting ability and physical appearance she is currently a sought-after young Hollywood actress which is apparent by her roles in Blade: Trinity (2004) and Stealth (2005). Producer Joel Silver has commented that Biel was his first choice to play the title role in writer-director Joss Whedon's Wonder Woman. After a nearly three year absence, Jessica surprised her fans by making one final appearance in the series finale of 7th Heaven in May 2006 - however, seeing as how the series has been renewed for another season, Jessica's character might return for subsequent episodes in the future.

Jessica attended the exclusive private school the Lycée Français de Los Angeles for high school. In fall 2000, she enrolled in undergraduate study at the premier liberal arts school, Tufts University in Medford, Massachusetts. She left before completing a degree program in order to be able to concentrate on her acting career.

Biel's hobbies include ballet, soccer, running, yoga and hiking. She has a dog named East. She recently bought a house close to her parents in Colorado. Biel is the co-founder of MTDN (Make the Difference Network) and she supports several non-profit groups, including PETA and the home rehabilitation organization Rebuilding Together.

Biel currently resides in Los Angeles. She dated actor Chris Evans during a time from 2001 to 2006, with at least one time "off" during that period. Together, they starred in the films London and Cellular.