Born in Huamachuco District, he discovered a great deal about the native Peruvians, learning about their way of life. This understanding of how they were oppressed was the focus for his novels. He attended classes at the University of Trujillo, and worked briefly as a journalist for the newspaper El Norte.

In 1930 Alegría joined the Aprista movement, dedicated to social reform as well as improving the welfare of native Peruvians. He was imprisoned several times for his political activities before finally being exiled to Chile in 1934.

He remained in exile in both Chile and later the United States up until 1948. Later, he taught at the University of Puerto Rico, and wrote about the Cuban revolution while in Cuba. His most well known novel, Broad and Alien is the World (1941) or El mundo es ancho y ajeno, won the Latin American Novel Prize in 1941, and brought him international attention. It depicts an Andean community, living in the Peruvian highlands. The book was later published in the United States and has been reprinted many times, in multiple languages.

Alegría returned to Peru in 1957. He joined President Fernando Belaúnde Terry's party (Acción Popular) and was elected to the Chamber of Deputies in 1963. He died unexpectedly in Lima, Peru on February 17, 1967. After his death, his widow published many of his essays and reports he had written for various newspapers. He was 58 years old.

Broad and Alien is the World has been recently published ISBN 0850362822 by Merlin Press of the United Kingdom.