As a teenager, O'Donnell started modeling and acting in commercials before landing his first feature film, Men Don't Leave, in 1990. As he made a name for himself in a succession of films in the early '90s, O'Donnell appeared in prestigious projects with seasoned actors, two of whom won Oscars for their work (Al Pacino for Scent of a Woman and Jessica Lange for Blue Sky). Having earned heartthrob status, he took on diverse roles, including parts as a conflicted attorney in The Chamber, a young Ernest Hemingway in the flop In Love and War and Robin in two critically reviled Batman movies. A break in his film career allowed O'Donnell to focus on his personal life, marrying his longtime sweetheart and becoming a father. Turning his attention to the small screen in the 2000s, he revived his career with recurring roles as a murderer on The Practice and as a sexy veterinarian on one of TV's most popular series, Grey's Anatomy. In 2009, he took on the starring role of special undercover agent Callen on the spin-off series NCIS: Los Angeles.