Swain was born on August 12, 1980 in Malibu, California, the daughter of Cindy and David Swain, Sr., an electrical engineer. She has two sisters, Chelsea (born 1982/1983) and Alexis (born 1978/1979), and a stepsister and -brother from her father's first marriage. Swain grew up in Malibu where she attended Malibu High School, and enjoyed playing sports, making art, and listening to music. Swain excelled at learning, earning straight A's and becoming Valedictorian like her sister before her. Her parents are separated.
Swain started her career in Hollywood as a stunt double; she appeared under the ice as Macaulay Culkin's younger sister in Joseph Ruben's The Good Son (1993). In 1995, at the age of fourteen she was chosen out of 2,500 girls to play the title role in Adrian Lyne's controversial second screen adaptation of Lolita (1997 film) as Lolita Dolores "Lolita" Haze. She was 15 during filming and her performance was praised by critics. She later then played the rebellious teen "Jamie Archer" in John Woo's Face/Off (1997). She starred in the drama filmGirl in which she plays a high-schooler who is determined to lose her virginity in 1998. In 2009, Swain appeared in Starz Inside: Sex and the Cinema which discussed the depiction of sex in film. That same year, she was featured in the movie Noble Things, a movie about the country star Jimmy Wayne Collins, which also starred country musician Lee Ann Womack. Swain also starred in the horror/slasher film Fall Down Dead as the main character, Christie Wallace. She starred in Monte Hellman's romancethrillerRoad to Nowhere in 2010. In 2011, Swain was featured in David Ren's action thriller The Girl from the Naked Eye. She starred in the direct-to-videoscience fiction filmNazis at the Center of the Earth in 2012. In 2013, Swain starred in Gregory Hatanaka's drama film Blue Dream as Gena Townsend.
In 1998, Swain was in a relationship with Charlie Bambrook. Swain was in a relationship with Dean Paraskevopoulos from 2001-2003. She was then in a relationship with Justin Strock from 2006-2007. She was engaged to producer Andrew Bennett in 2008. She has been in a relationship with director/screenwriter Marc Clebanoff since 2012.  Swain was ranked #63 in the FHM's top 100 hottest women in the world found in the June 2001 issue of FHM. Stuff Magazine selected her as #79 out of 102 sexiest women in 2007.