In his teens, Kieran began taking on leading roles in various indie films, while still continuing to appear in mainstream movies. His work on the film Igby Goes Down, also starring Susan Sarandon, Ryan Phillippe, and Bill Pullman, earned him a Golden Globe nomination. His younger brother, Rory, also acted in the film, playing the younger version of Kieran’s character, Igby. In 1999, Kieran received critical acclaim for his work in the Oscar-nominated movie Music of the Heart, alongside Meryl Streep, followed by teen comedy She's All That, as well as The Cider House Rules. His portrayal of a Catholic altar boy in the 2002 Indie film The Dangerous Lives of Altar Boys, with Jodie Foster, was also met with critical acclaim.

Growing up in New York City, Kieran shared a cramped apartment with his siblings, Macaulay, Rory, Quinn, Christian, Shane, and Dakota. After their parents, Christopher "Kit" Culkin and Patricia Brentrup split, the children were caught in the center of a bitter custody battle. Though their mother was eventually awarded legal custody of the children in 1997, the tug-of-war took its toll on the children, and by this time, Kit Culkin had earned a reputation in the show business circuit as a ruthless stage parent who saw his children as mini money-makers to be profited from. Kieran once commented, "I certainly had a better, less hectic life than Mac. He took all the pressure at home and on movie sets. My dad basically left me alone because I wasn't making enough money to warrant his scrutiny."

In 2002, Kieran took to the stage in London’s West End, performing in This is Our Youth. He has continued with stage work in recent years, appearing in 2005 in the off-Broadway dark comedy After Ashley, alongside Anna Paquin. One year later, Culkin teamed up with Paquin again, this time on the big-screen, in the Kenneth Lonergan film Margaret, also starring Matt Damon.

YUDDY