Shane West (Shannon Bruce Snaith) was born in Baton Rouge, Louisiana, the son of Leah Catherine (née Launey) and Don Snaith. His mother is a lawyer; his father, who was born in Jamaica, is a drugstore owner. Both parents were musicians and had their own punk bands. He is of Cajun French descent through his mother. He is the eldest of three children with a sister Simone and a half-sister Marli Ann. His parents divorced in 1982 when he was four years old. Influenced by his parents, he grew up listening to The Clash, The Jam, Blondie, Elvis Costello, and The Kinks. He revealed: "I always thought I would be doing music rather than acting."

At the age of ten, West and his sister Simone moved to Compton, California with their mother because she was looking for a better job and then they moved to Norwalk, California. When he was fifteen or sixteen, West moved to Los Angeles to pursue an acting career where he struggled for two years and lived at his manager's house. West made his acting debut in 1995, appearing in the CBS drama Picket Fences in season 4: episode 6 titled "Heart of Saturday Night", where he played Dave Lattimore

In 1998, West guest-starred in several television series including Buffy the Vampire Slayer, and played Mark Tapper in the stage production of The Cider House Rules before landing his first major role in 1999 in the ABC family drama Once and Again, playing Eli Sammler for three seasons. West's feature film debut was in Liberty Heights, a film about a Jewish family in Baltimore, directed by Barry Levinson. He also co-starred in the teen comedies Whatever It Takes (2000) and Get Over It (2001).

West was subsequently cast as Landon Carter opposite singer and actress Mandy Moore in 2002's adaptation of Nicholas Sparks' novel A Walk to Remember, which was a modest box office success, grossing over $41 million in the United States. Roger Ebert of the Chicago Sun-Times found him "quietly convincing". His performance in the film earned him a Teen Choice Award for Choice Chemistry with Moore. He also appeared in the Mandy Moore music video "Cry". That year, West won the Young Hollywood Award Male Superstar of Tomorrow.

In 2003, West starred as an adult version of Mark Twain's Tom Sawyer in The League of Extraordinary Gentlemen alongside Sean Connery. The film was a commercial success, earning over $179 million worldwide from a production budget of $78 million. A year later, he joined the cast of the NBC long-running medical drama, ER at the eleventh season premiere, playing resident Ray Barnett. In May 2007, West left ER at the end of the thirteenth season after winning a role in Supreme Courtships, but the series was not picked up by the Fox Network. In October 2008, West returned to ER for three episodes during its fifteenth and final season.

During the hiatus between seasons of ER, West worked on shooting the independent film What We Do Is Secret, which premiered at the 2007 Los Angeles Film Festival after much delay. West helped to finance it. In the film, he portrays Darby Crash, a member of the 1970s punk band The Germs. Members of the band were impressed by West's performance and re-formed the band with West taking the deceased Crash's place. West received positive reviews for his portrayal; the San Francisco Chronicle stated that he is the one who "lifts the entire film to a whole other level". Similarly, the Seattle Times wrote that his impersonation was "worth saluting" while TV Guide called it "pretty impressive". In 2008, he received the Rising Star Award in Philadelphia Film Festival for his work in What We Do is Secret. West starred in The CW spy drama Nikita from 2010 to 2013. See him now on Sundays on Salem at 10/9c on WGN America.