The Chicago-area native began his career as a juvenile model after learning that a female classmate earned $60 for a session. Armed with head shots and determination, the blond, blue-eyed O'Donnell soon landed print ads for Marshall Field's department stores. Local TV commercials soon followed before he landed his first professional acting role in a 1986 episode of the ABC series "Jack and Mike" (which was shot in Chicago). Although he preferred to attend crew practice than audition for his breakthrough debut screen role as Jessica Lange's teenage son in "Men Don't Leave" (shot in 1988; released in 1990), O'Donnell subsequently nailed the part and his career began to blossom. He was briefly seen in "Fried Green Tomatoes" (1991) as the doomed brother of Idgie Threadgoode (Mary Stuart Masterson) and offered a fine turn as a preppie rooming with a Jewish student (Brendan Fraser) in "School Ties" (1992), roles which typecast him.

"Scent of a Woman" (1992) also played off his altar-boy looks, casting him as a student reluctantly shanghaied into accompanying a belligerent blind military officer (Al Pacino) to NYC. Although Pacino's histrionics threatened to blow him off the screen, O'Donnell managed to hold the screen, projecting a quiet strength that fit the character. Attempting to shift gears, the actor accepted the role of the callow D'Artagnan in yet another remake of "The Three Musketeers" (1993) but he was upstaged by his more flamboyant co-stars Charlie Sheen and Kiefer Sutherland as well as an ill-advised curly hairdo. Rebounding, O'Donnell tapped his familial Irish roots to portray a big man on campus who catches the eye of an overweight dreamer in "Circle of Friends" (1995). Further honing his chops as a romantic leading man, he was paired with wild child Drew Barrymore in "Mad Love" (also 1995) in Antonia Bird's study of a misunderstood teenage couple. With the same year's revisionist "Batman Forever", O'Donnell allowed his natural charisma to come to the fore as circus acrobat Dick Grayson whom he essayed with the right notes of rebellious cockiness that played off Val Kilmer's stoic Caped Crusader. Attempting to stretch his thespian muscles further, he stumbled as an inexperienced lawyer attempting to save his racist grandfather from Death Row in "The Chamber" and was miscast as the young Ernest Hemingway (opposite Sandra Bullock) in the biographical romance "In Love and War" (both 1996). Following a reprise of his sidekick (this time to George Clooney) in the overproduced and confusing mess "Batman & Robin" (1997), O'Donnell withdrew from showbiz to get married and enjoy quality time with his bride. He returned to the screen as a goofy deputy investigating a possible homicide while romancing the deceased's granddaughter in Robert Altman's Southern Gothic comedy "Cookie's Fortune" (1999). Later that year, under the auspices of his George Street Films, he made his producing debut on "The Bachelor", a romantic comedy loosely based on the 1925 Buster Keaton vehicle "Seven Chances". In the film, O'Donnell starred as a reluctant groom who must marry within a 24-hour period in order to inherit his grandfather's multi-million dollar estate. He then segued to the action adventure "Vertical Limit" (2000), playing a mountaineer who comes out of retirement to save his sister who is trapped in a vertical cave on a climb in the Himalayas.