Bernal was born in Guadalajara, Jalisco to Patricia Bernal (an actress and former model) and José Ángel García (an actor and director). His stepfather is Sergio Yasbek, who his mother married when he was young. Gael speaks Spanish, Italian, French, and English. He is also a close friend of actor Diego Luna. Bernal started acting as a one-year-old and spent most his teen years starring in soap operas.

Bernal was becoming a soap-opera heartthrob, but at age 19, he left Mexico's television world to study acting at the Central School of Speech and Drama in London, UK. Subsequently, Bernal has starred in some of Mexico's most celebrated recent films, beginning with Amores Perros (2000), then 2001's Y Tu Mamá También, and El Crimen del Padre Amaro (2002). It was his debut as a working-class street thug in the Oscar-nominated Amores Perros that first grabbed Hollywood's attention. He has also done some theatre work, including a 2005 production of Bodas de sangre ("Blood Wedding"), by Federico García Lorca in the Almeida theatre, London. Bernal also portrayed Cubano revolutionary Che Guevara in 2004's The Motorcycle Diaries, an adaptation of a journal a 23-year-old Guevara wrote about his travels across South America.