Rory Culkin was born in New York City, New York. He is the youngest son of Kit Culkin, a former stage and child actor, and Patricia Brentrup. He is the brother of Shane Culkin, Dakota Culkin, Macaulay Culkin, Kieran Culkin, Quinn Culkin, and Christian Culkin. His mother, who is from North Dakota, is of German and Norwegian descent. His father, from Manhattan, has Irish, German, English, Swiss-German, and French ancestry.

He grew up in New York along with his mother (his parents split up in 1995) and the rest of his siblings. He started his career by playing younger versions of his brothers in their films, such as Richie Rich and Igby Goes Down. He landed his first real role in 2000 in the Kenneth Lonergan film You Can Count on Me. Rory Culkin is best known for his work in the 2002 M. Knight Shyamalan film Signs but has also appeared in a number of independent films like Mean Creek, The Chumscrubber, Down in the Valley, The Night Listener, and Lymelife. He has also appeared in some television shows such as The Twilight Zone and Law & Order: Special Victims Unit.