The daughter of New York State Assemblyman Edward G. Sullivan, who represented the Upper West Side's 69th district between 1977 and 2002, Sullivan majored in theater at Chicago's Northwestern University, spending a year of her studies in London. After graduation, the fledgling actress moved to Los Angeles, making her small-screen debut in an episode of oddball sitcom "Herman's Head" (Fox 1991-94). Balancing guest appearances on shows such as family drama "Party of Five" (Fox 1994-2000) and short-lived soap opera "Models Inc." (Fox 1994-95) with day jobs that included waitressing and working in a chocolate factory, Sullivan landed a spot in the cast of the newly-commissioned "Saturday Night Live" competitor "MADtv" in 1995. Sullivan remained on "MADtv" until 2001. Her most famous recurring characters included the horrifically conceited Vancome Lady and racist country singer Darlene McBride. One notable sketch sent up actors who audition for the long-running police procedural series "Law & Order" (NBC 1990-2010); ironically, Sullivan would herself later appear on the spin-off "Law & Order: Special Victims Unit" (NBC 1999-). While working on the sketch comedy series, Sullivan also began performing voiceover work for animated shows. Her voice-only credits included various characters in Seth MacFarlane's animated hit "Family Guy" (Fox 2000-) and a supporting role in "Toy Story" spin-off series "Buzz Lightyear of Star Command" (UPN 2000-01). However, it was her "King of Queens" character, unlucky-in-love dog walker Holly Shumpert, that made Sullivan's mark with the widest audience. Though never a full-time cast member, Sullivan appeared on around a quarter of the episodes in the entire series, and her charm and comic subtlety made her endearing character a strong fan favorite. Sullivan also played recurring roles on three sitcoms created by her friend Bill Lawrence: on "Scrubs" (NBC 2001-08, ABC 2009-10), she played regular patient Jill Tracy; on the short-lived animated series "Clone High" (MTV 2002-03), she played a teenage Joan of Arc; and on "Cougar Town" (ABC 2009-12, TBS 2013-15), she played Jules' (Courteney Cox) perpetually frazzled therapist Lynn Mettler.Sullivan earned her first shot at a headline sitcom role with Lifetime's "Rita Rocks" (2008-09), in which she played a married suburban mother of two who starts a garage band; she also sang lead vocals on the show's theme song, "Somebody to Worry About." In 2009, she continued her voiceover career with the supporting role of Marlene the otter in the animated film spinoff "The Penguins of Madagascar" (Nickelodeon 2009-). In 2013, she co-starred in the young-adult sitcom "Wendell and Vinnie" as aggressive, driven lawyer Wilma Bassett, older sister of adult slacker Vinnie (Jerry Trainor), who has become the legal guardian of his adolescent nephew Wendell (Buddy Handleson).