Prior to this success, he acted in a 1991 episode of the New York City-lensed TV series "Law & Order" and appeared the following year in the feature "Scent of a Woman". A regular role on the ABC sitcom "Phenom" (1993-94) landed the actor in Los Angeles, where he essayed the part of the title teen tennis star's older brother. The series was a forgettable venture, but Louiso stayed busy, with voice acting roles on Fox's "The Critic" and Nickelodeon's "AAAHH!!! Real Monsters" (both 1995). That same year he was featured in the hit feature "Apollo 13" and the USA Network's TV-movie thriller "Letter to My Killer". In 1996 he racked up more feature credits, appearing in "The Rock" and "Jerry Maguire", making a particularly strong impression as a jazz-loving nanny in the latter. He co-starred in 1997's abominable comedy "8 Heads in a Duffel Bag", playing the ill-at-ease medical student roommate of David Spade's snarky character, unwittingly caught up in an unfathomable mix up with a hit man.
A recurring role as the uptight and conscientious assistant to Dr Lisa Catera (Stacy Edwards) on "Chicago Hope" followed in 1998, and the popular CBS drama introduced the actor to a large audience. The following year he returned to the big screen with a role in the little seen drama "A Cool, Dry Place" before impressing moviegoers with his featured role opposite John Cusack, Jack Black and Lisa Bonet in the irreverent romantic comedy "High Fidelity" (2000). Stephen Frears' Chicago-set adaptation of British author Nick Hornby's novel featured Louiso as Dick, a shy and awkward record store clerk with a specialized knowledge of pop music and a gentle, almost shrinking demeanor. He gave an impressive co-starring performance in the hit film, and took the odd role to delightfully charming heights in a scene-stealing turn that marked him as a performer on the ascent.