Making his feature debut in 1989's modern-day hippie comedy "Rude Awakening", Eigenberg followed up with a small role in the 1990 comedy "In the Spirit" and a supporting turn in the 1991 independent psychodrama "By a Thread". The actor disappeared from the big screen until 1998's "A Perfect Murder" but stayed busy with television work. An early supporting turn in the "HBO Showcase" presentation "Daybreak" aired in 1993, and Eigenberg was next used to good effect on an especially memorable episode of "Homicide: Life on the Street" (NBC, 1996), playing an all-too-enthusiastic witness to a sniper attack who turns out to be the murderer. Eigenberg next surfaced on the ABC legal drama "The Practice" with a recurring 1997 stint as a district attorney. He proved something of an unlikely action hero as a regular on the syndicated action series "S.O.F Special Ops Force" (1998) before commencing his run as Steve.

Impressing the devout viewers of "Sex and the City" with his adorably strong but vulnerable take on Steve, Eigenberg had begun his breakthrough, though a regular series role in Tom Fontana's police drama "The Beat" (UPN, 2000) didn't jumpstart his career as one might have predicted since the show was cancelled after only six airings. The actor had a 2001 recurring role on NBC's "Ed" as the genius romancer of the two single female leads (Julie Bowen and Leslie Boone) and was featured the following year in his biggest film role to that point, as a journalist colleague and friend to Richard Gere in Mark Pellington's eerie thriller "The Mothman Prophecies".