Like many model, Grieco harbored dreams of an acting career and on his first TV audition was cast as skiing playboy Rick Gardner on the ABC daytime drama "One Life to Live", a role he played for about a year (1986-87). Heading west. he soon landed occasional guest appearances, most notably a 1987 episode of "Who's the Boss?" as a long-lost cousin of Tony (Tony Danza). A guest stint on "21 Jump Street" led to a contract as a regular in 1988, just as Johnny Depp, eager for other opportunities, had scaled back his hours to occasional appearances. Grieco partly replaced Depp as the show's heartthrob, which led in part to his headlining the spin-off "Booker", which lasted only one season (1989-90). Shifting to features, he made his debut as a class clown mistaken for an undercover agent in Paris in the disappointing "If Looks Could Kill" (1991). His second film, the highly-touted "Mobsters" (1991) teamed the actor with the similarly then-hot Christian Slater and Patrick Dempsey. Cast as Benjamin 'Bugsy' Siegel, Grieco offered a modest turn that was partly overshadowed by Warren Beatty's more high profile biopic "Bugsy" (also 1991). Two years later, he was cast as a wheelchair-bound dancer who gets a second chance and becomes a lout in "Tomcat: Dangerous Desire" (1993), but most of his subsequent films have been standard action fare, such as "Under the Gun" (1995) and "The Demolitionist" (1996). "Heaven or Vegas" (lensed 1996), which cast the actor as a gigolo romancing a prostitute (Yasmine Bleeth) tried to play off the off-screen pairing of its stars, but as of 1998 remained without distribution.
Grieco found steadier employment on the small screen. He was a street racer who falls in love in "Born to Run" (Fox, 1993), while in "Sin and Redemption" (CBS, 1994), he was the rapist from a woman's past who marries her. In "A Vow to Kill" (USA, 1995), Grieco was a new groom who goes on his honeymoon and then tries to extort money from his father-in-law by claiming both he and his bride had been abducted. He was a domestic abuser in "It Was Us or Them" (CBS, 1995) and a time traveler in "When Times Expires" (The Movie Channel, 1997). He fared less well with a return to series TV in the short-lived UPN drama "Marker" (1995).