Karen Jane Allen was born in Carrollton, rural southern Illinois, to Patricia (Howell), a teacher, and Carroll Thompson Allen, an FBI agent. She spent her first 10 years traveling around the country with her parents and two sisters. She was always "the new girl in school." Acting did not really cross Allen's mind until she was in her early 20s, when she saw a Jerzy Grotowski theater production that impressed her so much, she instantly decided to give it a shot. She trained as a classical actress and enrolled at the Actors Studio and with Lee Strasberg in New York City. During this period, she made several student films and directed and acted in several plays. In 1976, she made her first film appearance in the award-winning small film The Whidjitmaker (1976).

Her first major film role came as Katy in 1978's National Lampoon's National Lampoon's Animal House (1978), which became one of the biggest hits of the year, obtained "classic" status, and launched a whole host of young "hot" stars. However, shortly after National Lampoon's Animal House (1978) opened, Allen was struck by a rare and dangerous eyesight condition called keratoconjunctivitis. Luckily, the condition subsided and Allen could continue her dramatic rise to the top. Lead roles in cult favorites like The Wanderers (1979) and the controversial thriller Cruising (1980) followed, as did smaller parts as in Woody Allen's Manhattan (1979). However, it was her performance in Rob Cohen's A Small Circle of Friends (1980), as well as her previously mentioned turn in National Lampoon's Animal House (1978), that caught the eye of a certain Steven Spielberg. He then cast her as the feisty heroine and co-star of Harrison Ford in his big-budget blockbuster Raiders of the Lost Ark (1981), which became a huge hit in 1981-82 and is regarded by many film buffs as the greatest action-adventure film ever made.

Following the huge success of Raiders of the Lost Ark (1981), Allen chose to spend more than two years out of the limelight, concentrating on smaller, more personal projects. She won a major award for her performances on Broadway, won critical acclaim for her portrayal of Abra in the hugely successful ABC production of East of Eden (1981), and had parts in two smaller films: Alan Parker's Shoot the Moon (1982) and Split Image (1982), co-starring James Woods and Peter Fonda. She returned to the mainstream in 1984 with Until September (1984) and Starman (1984), co-starring Jeff Bridges and directed by John Carpenter (of Halloween (1978) fame), but once again decided to leave the limelight for a couple of years to do more stage work and some troubled indie films. While Allen has worked almost constantly since then, giving notable performances in Paul Newman's screen adaptation of The Glass Menagerie (1987), the Christmas hit Scrooged (1988), and Steven Soderbergh's underrated King of the Hill (1993), she has not been able to scale the same dizzy heights as the early 1980s hits. Most of her lead roles in feature films since Starman (1984) have not been that well-received (Animal Behavior (1989), Ghost in the Machine (1993), and The Turning (1992) among them). However, she has been seen to good effect on TV in such films as Challenger (1990), in which she portrayed tragic schoolteacher Christa McAuliffe, and All the Winters That Have Been (1997), co-starring Richard Chamberlain.

She has also made special guest star appearances on such shows as Law & Order (1990), Knots Landing (1979), and Alfred Hitchcock Presents (1985), and in several TV movies, including Hostile Advances: The Kerry Ellison Story (1996) and Secret Weapon (1990). She also played the lead in the CBS series The Road Home (1994). Karen Allen was married to soap star Kale Browne (with whom she co-starred in 'Til There Was You (1997)) in 1988 and they have a son, Nicholas. Apart from acting, Allen is also an accomplished singer, songwriter, and musician. She played in a band with Kathleen Turner, and recorded a duet with Jeff Bridges for the Starman (1984) soundtrack album.

She also writes plays, screenplays, and poetry; owns her own Ashtanga yoga enterprise; and spends time at her Berkshire Mountains farm or Upper West Side Manhattan townhouse. The classically trained actress also has a screenplay called "The Second Coming," which is about to be made into a movie. Most recently she has starred opposite Peter Coyote in The Basket (1999), and appeared in the blockbuster The Perfect Storm (2000), in which she co-starred with George Clooney, Mark Wahlberg, and Diane Lane. In addition to these, she is working on Shaka Zulu: The Citadel (2001) and recently made an independent film, In the Bedroom (2001). Karen Allen is undoubtedly one of the most talented, ambitious, and versatile actresses of the last 20 years. In many ways, her own choices to "go back to theater and smaller projects" are the only things that have really stopped her being a major, major star. Allen was voted one of the most beautiful women in the world in 1983, and is a naturally attractive lady - who often plays characters significantly younger than herself. She also often plays unglamorous types - and there is no one better at portraying real, human, and wholly believable people.