María Jóhannsdóttir was born and grew up in western Iceland as the daughter of a poor widow. At the age of seventeen, she travelled to Reykjavík to take her upper secondary school leaving examination, but gave up and trained as a nurse instead.
She died of tuberculosis. Her debut novel Systurnar i Grænadal, 1908, examines major philosophical questions such as the existence of God and the conditions of love. The novel alternates between letters, poems, and motifs from popular belief; it is characterised by the modern Romantic taste for the melodramatic. María Jóhannsdóttir also published a number of poems and short stories in periodicals.