Britta Gröndahl, née Maartman, was born in Eskilstuna, Sweden, to Hans Maartman, a local politician, and his wife, Dagmar Tideman. In 1931, she was one of the few young women to earn a grammar school degree in Latin. She was unable to fulfill her desire to study political science, as it was not considered an appropriate subject for women of her day. She took up language studies instead and became a translator. In 1936, she married Gustav Gröndahl, a cellist, with whom she had three daughters. In the 1950s, she began researching socialism, and published her first book, a biography of Pierre-Joseph Proudhon, in 1959, launching her as an historian and journalist. She was active in the Swedish syndicalist movement, particularly the Sveriges Arbetares Centralorganisation (SAC), during a major part of her life. She In 1962, she travelled to Spain for the first time and eventually served as an important liaison between the Swedish and Spanish workers groups. In her memoir Äventyrens år (1994), she described how one of her assignments was to act as a courier, smuggling large sums of money into Franco's Spain for the clandestine Confederación Nacional del Trabajo, a Spanish confederation of anarcho-syndicalist labor unions.
She worked as a foreign correspondent for Arbetaren, the SAC publication, during the May 1968 student uprisings in Paris. In 1974, she witnessed and reported on the "Carnation Revolution" in Portugal. She translated the works of Michel Foucault, Marie Cardinal, and Claire Bretecher during the 1980s. She also operated an anarchist bookstore in Stockholm.