A former child model, he segued to acting with a 1987 guest appearance on "Highway to Heaven" and soon added roles in "Charles in Charge" and "Punky Brewster" to his resume. His success as the scheming Zack led to a primetime spin-off "Saved By the Bell: The College Years" (NBC, 1993-94) and several TV-movies based on the series. Gosselaar branched out to serve as creative consultant and host of the short-lived NBC game show "Brains and Brawn" (1993) before trying to make the move to films. Unfortunately, most of his efforts were in low-budget genre fare that moved directly to video (i.e., "Twisted Love" 1995). The actor found a niche playing against type (and often with dark hair) in more dramatic TV-movies along the lines of his accused rapist in "She Cried No" (NBC, 1997) before heading to the big screen as a wealthy student with poor grades who seeks a loophole in the uneven comedy "Dead Man on Campus" (1998).
Gosselaar then returned to the small screen to play a successful software developer who returns to his hometown with mixed results in "Hyperion Bay" (The WB, 1998-99). A follow-up series, the youth-minded political drama "D.C" (The WB, 200)) failed to score, but Gosselaar's career fortunes soared when he was tapped to replace Rick Schroeder as the new young partner of Det. Sipowicz (Dennis Franz) on "NYPD Blue" in 2001. As the stand-up young detective John Clark, Jr., who has issues with his ex-cop father and ultimatley turns to Sipowicz as a surrogate, Gosselaar impressed audiences and remained a fixture on the series until the end of its run in 2005.