Maria Isabel Barreno was born in Lisbon, Portugal, and graduated from the University of Lisbon with a degree in history and philosophy. She became a writer and a leader of the Portuguese feminist movement. She was most famous as one of the "Three Marias," along with Maria Teresa Horta and Maria Velho da Costa. 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 Isabel Barreno also worked as a journalist, at the National Institute of Industrial Research, and as a cultural adviser at the Portuguese embassy in Paris. She was the author of more than 20 novels and collections of short stories in her career.