Lancaster was born and raised in Overland Park, Kansas, alongside her younger brother Daniel; parents Barbara and Michael were a homemaker and a real estate agent, respectively. Eventually, Michael's job moved the Lancaster family to Mission Viejo, California, where Sarah took up acting classes with R. J. Adams at The Actors Workshop.

Sarah's abilities landed her a talent agent, who helped the then-eighth grader to secure her first series-regular role on Saved by the Bell: The New Class in 1993. During this time, she was tutored on the set and took college courses at the University of California, Irvine to expedite her graduation from high school. After graduation from New Hart Jr. High, she moved to Los Angeles to further her acting career.

Sarah racked up other guest-starring roles, on shows such as: Dawson's Creek, That '70s Show, Scrubs, and CSI: Crime Scene Investigation. She also landed two recurring roles: on The WB series, Everwood, as Ephram's love interest Madison Kellner; and on David E. Kelley's FOX series, Boston Public.

Lancaster has also worked as a jealous girlfriend-turned-serial killer in the movie Lovers Lane...and as the blackjack dealer, Veronica Harold, on CBS's short-lived Dr. Vegas.

Lancaster's other talents include eight years of training in jazz and funk dancing.

Sarah is no relation to late acting great Burt Lancaster, although she admits to being asked about him a lot.

She says growing up in Kansas led her to become a fan of the Kansas Jayhawks basketball team. Lancaster says she never cared for the football team but their run to the 2008 Orange Bowl made her a bandwagon fan.

She says she has a tattoo but adds she is too shy to admit where it is located.