Born the eighth of 11 children of a Viscayan miner, Ibárruri was compelled by poverty to quit school at age 15 to work as a seamstress and later as a cook. Becoming radicalized, she published in 1918 an article in a newspaper called El Minero Vizcaino, using for the first time the pseudonym La Pasionaria. Two years later she joined the newly formed Spanish Communist Party. After a turbulent career, in which she was jailed several times for political activities, she emerged as one of the Communist deputies in the Republican parliament and, by the outbreak of the Civil War in 1936, had become a national figure. A sometimes violent radio and street orator, she made such famous exhortations as “It is better to die on your feet than to live on your knees” (July 1936).

With Francisco Franco's victory in 1939 she escaped by plane to the Soviet Union, where over the years she represented her party at Kremlin congresses, until Santiago Carrillo succeeded her as secretary-general in 1960. Though reputed to be an old-line Stalinist, she protested the Soviet invasion of Czechoslovakia in 1968. She returned to Spain on May 13, 1977, some 18 months after Franco's death and 34 days after the Spanish government again legalized the Communist Party. She was reelected to her deputy seat in the Spanish parliament that year but later resigned because of ill heath. She remained honorary president of the Spanish Communist Party until her death. Throughout her career Ibárruri almost always appeared dressed in black.

She married Julián Ruiz in 1915 and separated from him in the 1930s. Only two of her six children survived childhood; a son, Rubén, was killed at Stalingrad as an officer in the Red Army. In 1962 she published her memoirs, El único camino (“The Only Way”; Eng. trans., They Shall Not Pass).