Quickly becoming a mainstay thanks to her talent at showing the wackiness behind unnaturally earnest characters such as NPR radio host Mary Jo and over-enunciating middle school music department singer Bobbi Mohan-Culp, who along with husband Marty (Will Ferrell) presents a medley of fantastically butchered popular songs. A violinist and trained singer, Gasteyer often worked on vocalist characters, including beleaguered folk singer Cinder Calhoun and pop diva Celine Dion. The former performance earned the actress a spot on the real-life female folk tour Lilith Fair in 1998 while the latter impersonation landed her a spot on the special "VH1 Divas Live '99". Gasteyer's success on the series would help to combat the behind-the-scenes boys' club mentality "SNL" was accused of perpetrating, while her impersonations and original characters would inform popular culture much like Mike Myers' Wayne Campbell, Eddie Murphy's Mister Robinson and Gilda Radner's Roseanne Roseannadanna had done in the past.
Gasteyer has racked up credits outside the domain of "Saturday Night Live", beginning with the 1995 feature film "Courting Courtney" (released 1998). She acted in the famed "soup Nazi" episode of "Seinfeld" (NBC) in 1995, and appeared on "Hope & Gloria" and "Party of Five" the following year. A memorable role as a rodent wrangler in the 1998 Disney live-action feature "Meet the Deedles" offered the actress more screen time, while 1998 appearances on the NBC series "Mad About You" and "Law & Order" made her a familiar face to those who stuck to primetime. That same year she had a significant guest stint on "Just Shoot Me" as a baby-talking nanny who gets into some adult situations with her boss' assistant (David Spade). Larger roles on the big screen followed. Gasteyer played Nixon's loyal secretary Rosemary Woods in the Watergate satire "Dick" (1999) and was featured the following year in the provocatively titled comedies "Woman on Top" and "What Women Want". 2001 saw Gasteyer hit the big screen again in the comedy "What's the Worst That Could Happen?", starring Danny De Vito and Martin Lawrence.