Born to P.J. Barry and Dolores Du Bois on November 29th 1965 in New York, New York, USA, Neill made his screen debut at the tender young age of 13 in the 'Martin Davidson' comedy Hero at Large (1980), opposite _"Three's Company"_ star John Ritter and a very youthful Kevin Bacon. Next came along the horror flick Amityville III: 3-D (1983), in which another star to be Meg Ryan featured in a brief part. After a major role in Old Enough (1984), Neill got his first top billing part, in which should have been his breakthrough role, as Joseph King, Jr. in Joey (1986), where he delivered a very moving performance as the basic run of the mill rebel without a cause! Following the Robert Altman comedy _O.C. and Stiggs (1987)_, Neill showed his darker side with a duo of psychotic roles in the films Heat (1986) with Burt Reynolds and Fatal Beauty (1987) alongside Whoopi Goldberg, in which film critic Roger Ebert described as "not a great movie, but it has good qualities." His next film, Slipping Into Darkness (1988), was a very little seen independent film shot in Fremont, Nebraska, USA, where as Neill then shot an episode of the hit series 21 Jump Street (1987), before giving another towering performance as Jill Ireland's adopted son John, who tragically died of an accidental drug overdose in 1995, in the telefilm Reason for Living: The Jill Ireland Story (1991).

Over the next few years, Neill had a brief recurring role as Greg Parker in another hit series Melrose Place (1992), before returning to film with roles in O çok sevimli (1997), another little seen independent film Show & Tell (1998) and showed his penmanship skills by co-authoring the story for Friends & Lovers (1999), a film about a group of twentysomethings who hit the skiing slopes. Starring alongside Neill in the film was the likes of Stephen Baldwin, supermodel Claudia Schiffer and 'Robert Downey, Jr.'. Neill's older brother, Matthew Barry, is an actor and casting director, whereas his sister Nina Barry is an actress and casting associate. So far to date, his films have grossed over an estimated $U90,000,000.