Alejandro is the son of a Spanish mother and a Chilean father. His family moved back to Spain when he was 1 year old, and he grew up and studied in Madrid. He wrote, produced and directed his first short film La cabeza at the age of 19, and he was 23 when he directed his feature debut Tesis (1996). His film Open Your Eyes (1997) was a huge success in Spain and was distributed worldwide.

It was remade in Hollywood by Cameron Crowe as Vanilla Sky (2001), starring Tom Cruise, Penelope Cruz (also the star of the original version) and Cameron Diaz. The Others (2001) is Amenábar's first English language film.