Green's first movie role was in the 1984 film, A Billion for Boris. At eight, Green landed his first film assignment; a co-starring role in "Hotel New Hampshire" with Jodie Foster and Rob Lowe. He appeared in the 1987 film Can't Buy Me Love, playing the part of Patrick Dempsey's little brother, Chuckie Miller. He also starred in Woody Allen's Radio Days (1987) as Joe, and appeared in Big Business (1988) and, in the same year, in My Stepmother Is an Alien (with future Buffy co-star Alyson Hannigan). Green appeared in the miniseries It (as Richie Tozier, age 12), all three Austin Powers movies (as Dr. Evil's son, Scott), and Enemy of the State and The Italian Job as a computer specialist. He was also in the films Can't Hardly Wait and Without a Paddle.
 
 Green's first television appearances were in Tales from the Darkside and Amazing Stories in the mid-1980s. He made a few appearances on the 1980s television series The Wonder Years. He also appeared in commercials as the window cashier for Rally's Hamburgers in the early 1990s, sparking the catch-phrase, "Cha-Ching!". In 1994 he starred alongside Jennifer Love Hewitt in the shortlived series Byrds of Paradise.
 
 He worked with Hewitt again in 1998's Can't Hardly Wait , which also featured Paige Moss who would later play the female werewolf that seduces OZ into cheating on Willow in Buffy the Vampire Slayer. Amber Benson (Tara, Buffy) was also in this film, but her scenes were cut in order to get a PG-13 rating.
 
 Green also began appearing as Daniel "Oz" Osbourne the werewolf in the television series Buffy the Vampire Slayer during seasons 2-4. Green has also been featured in roles on Greg the Bunny, Tucker, The X-Files, That '70s Show, Will & Grace, Mad About Steve, Reno 911!, Entourage, and Grey's Anatomy.