Bell was born on July 18, 1980, in Huntington Woods, Michigan, a suburb of Detroit, where she was raised. Her mother, Lorelei (née Frygier), is a registered nurse, and her father, Tom Bell, works as a television news director in Las Vegas, Nevada. Her parents divorced when she was two years old, and she has two stepsisters from her father’s second marriage. She also has two half-sisters and two half-brothers from her mother’s second marriage. Her mother is of Polish descent and her father has German, Scottish and Irish ancestry.
Bell stated that she did not like her first name at the age of four. Bell’s mother convinced her to go by her middle name, Anne, instead; she used the name Annie until high school. Bell once broke both her wrists at the same time playing street hockey with friends.
Just before her freshman year of high school, Bell’s parents decided to remove her from the public school system.She attended Shrine Catholic High School in nearby Royal Oak, where she took part in the drama and music club. During her time at the school, she won the starring role in the school’s 1997 production of The Wizard of Oz, as Dorothy Gale and also appeared in productions of Fiddler on the Roof (1995), Lady, Be Good (1996), and Li’l Abner (1998). In 1998, the year she graduated, Bell was named the yearbook’s “Best Looking Girl” by senior class vote.
Shortly after her high school graduation, Bell moved to New York City to attend New York University’s Tisch School of the Arts, majoring in musical theater. In 2001, during her senior year, Bell left a few credits shy of graduating to take a role in the Broadway musical version of The Adventures of Tom Sawyer.
In 2006 and again in 2013, Bell was selected “World’s Sexiest Vegetarian” on PETA’s yearly poll. She was placed No. 68 on Maxim’s 2005 “Hot 100” list, No. 11 in Maxim’s 2006 “Hot 100” list, and No. 46 in Maxim’s 2007 “Hot 100” list in which she was stated to have “single-handedly saved The CW from becoming the worst network ever.” In 2006, Maxim also placed Bell at the top of the “Fall TV’s Criminally Sexy Investigators” List. In 2008, she was featured at No. 59 on AskMen’s Top 99 Women of 2008 List. Reflecting on her admitted popularity with “geeks”, Bell was voted the fourth-sexiest woman on TV by the staff at Wizard magazine.
Bell stated she never thought of herself as womanly because “I always play and look and act 10 years younger than I am.” However, she said, “Something magical happened when I turned 25—I looked in the mirror and was like, ‘You might not get carded for an R-rated movie anymore.’ Like I didn’t have a little stick figure anymore.” Bell has said that many of her characters are tomboys because she was “not homely enough to play the nerdy girl and not nearly pretty enough to play the pretty girl”.
Bell has been associated with the idea that “nerdy is the new cool”, and she explained, “what was previously perceived as nerdy is now viewed as original. What I like about nerdiness, geekiness, is it doesn’t really matter what you’re into—it just means you’re not a follower.” She has also said, “I love nerds. Comic-Con junkies are the tastemakers of tomorrow. Isn’t that funny? The tables have turned.” Vanessa Juarez of Entertainment Weekly commented that Bell’s roles on Veronica Mars, Heroes and as a Star Wars fanatic in Fanboys have “solidif[ied] her placement at the center of the geek universe,” while Rodney Rothman stated, “I guess she’s cornered the market on losers.” Bell’s work is often compared to Sarah Michelle Gellar’s portrayal of the title character on the cult television series Buffy the Vampire Slayer. Frank Scheck of The Hollywood Reporter stated that Bell was “arguably the television successor [to Gellar’s portrayal of Buffy] when it comes to fighting bad guys.” Bell is sometimes confused with Lauren Conrad from The Hills. “Yeah, sometimes fans yell, ‘Hey, Lauren’ to me, but usually from a distance,” said Bell.
Despite “new celebrity” status, Bell claimed that she was not concerned because “no one ever recognizes me anyway”. She has said that her friend Hayden Panettiere is more famous than she is and attracts more attention; as Bell explained, “I hang out with Hayden quite a bit—they never take pictures of me. I just step to the side, and I push myself in front of her when she wants to get out of it, or put her in the car.”
Bell was a recurring guest on The Late Late Show with Craig Ferguson, appearing in interviews as well as sketches. On The Late Late Show, she shows a humorous hostility towards Craig Ferguson’s robot skeleton sidekick Geoff Peterson, claiming that she had wanted to be Ferguson’s sidekick on his show and taking it upon herself to cut Peterson down every chance she gets. Both Bell and Peterson appeared with Ferguson during the five Late Late Show episodes filmed in France.
In January 2011, it was announced that Bell would be the new face of Neutrogena.
In 2019 Bell made the cover of Entrepreneur (April~May issue) in which Kristen talks about her company selling snack bars currently named This Saves Lives, the sales helps malnourished children around the globe get fed.