Martinson was born in Jämshög in southern Sweden. His father died when he was six, and his mother abandoned her seven children to emigrate to America. The rest of his childhood was spent in a succession of foster homes and/or children's homes (sources differ) and he was very unhappy. He ran away several times, and at 16 he went to sea as a merchant marine. He spent the next six years at sea and living and working at various unskilled jobs in India and South America, but returned to Sweden after contracting tuberculosis.
His books included fiction, some of it autobiographical and poetry. He was elected to the Swedish Academy in 1949 and won the Nobel Prize for Literature in 1974, jointly with fellow Swede Eyvind Johnson.