Maria Velho da Costa graduated from the University of Lisbon and worked as a secondary school teacher. She became a writer and a leader of the Portuguese feminist movement. She is most famous as one of the "Three Marias," along with Maria Isabel Barreno and Maria Teresa Horta. In 1972, the three women published Novas Cartas Portuguesas (The New Portuguese Letters), a book consisting of letters, essays, poems, and fragments using as a model the story of a famous 17th-century Portuguese nun, Soror Mariana Alcoforado. In its portrayal of the condition of women and female sexual expression, the book was considered a provocation and defiance of the Salazar regime's censorship. The authors were accused of pornography, arrested, and tried in a court case that lasted two years. The case was followed closely by the international press and feminists, who organized protest rallies at Portuguese embassies and consulates in London, Paris and New York. Eventually the three writers were acquitted. Maria Velho da Costa was a reader in the Portuguese and Brazilian Department of King's College, University of London, from 1980 to 1987.
She also served in cultural functions of the Portuguese government between 1979 and 1990. She has published numerous novels beginning in 1969 with Maina Mendes.