Macht was born in The Bronx, New York, the son of Suzanne Victoria Pulier, a museum curator and archivist, and actor Stephen Macht. He has three siblings, Jesse (who appeared on The Next Great American Band), Julie, and Ari Serbin. The family moved to California when Gabriel was five years old. After graduating from high school, he attended Carnegie Mellon College of Fine Arts.
Macht married actress Jacinda Barrett in 2004. The couple had their first child, a girl, Satine Anais Geraldine Macht, born August 20, 2007 in Los Angeles.
Macht was nominated for the Best Young Motion Picture Actor Award after playing his first role at age eight in the film Why Would I Lie? under the stage name Gabriel Swann. He has appeared in many film and television roles including A Love Song for Bobby Long, Because I Said So, The Recruit, and Archangel. Macht plays the title role in Frank Miller’s adaptation of Will Eisner’s comic creation The Spirit.