Javier Marías was born in Madrid. His father was the philosopher Julián Marías, who was briefly imprisoned and then banned from teaching for opposing Franco. Parts of his childhood were spent in the United States, where his father taught at various institutions, including Yale University and Wellesley College. His mother died when Javier was 26 years old. He was educated at the Colegio Estudio in Madrid.

Marías began writing in earnest at an early age. "The Life and Death of Marcelino Iturriaga", one of the short stories in While the Women are Sleeping (2010), was written when he was just 14. He wrote his first novel, Los dominios del lobo (The Dominions of the Wolf), at age 17, after running away to Paris.

Marías operates a small publishing house under the name of Reino de Redonda. He also writes a weekly column in El País. An English version of his column "La Zona Fantasma" is published in the monthly magazine The Believer.