Shlesinger is from Dallas, Texas, where she attended the private Greenhill School and participated on the school's Improv Team. She is Jewish. Shlesinger performed with ComedySportz Dallas. She attended the University of Kansas for her freshman year. She also participated in Semester at Sea. She then transferred to Emerson College in Boston and majored in Film. There she was a member of the campus' comedy sketch group, Jimmy’s Traveling All Stars, and refined her writing and editing skills. After graduating from college, she moved to Los Angeles to pursue stand-up. She was one of the most popular members of the "Whiteboy Comedy" group of stand-up comedians in Los Angeles which brought her to the stage at The Improv in Hollywood. Her ex-boyfriend is former NHL goaltender Jamie McLennan.
Shlesinger became the first female and also the youngest winner of NBC's Last Comic Standing in the series' sixth season. She was twice selected by other comedians to compete in the head-to-head eliminations and won both times. She appeared in The Last Comic Standing Tour.