Before his teens, Paz had joined the libertarian Ferrerist school Escuela Natura in Barcelona's El Clot working class district.

Following his 1937 arrest in a clash with Stalinists, he worked in a farm collective, wrote for the FAI's Tierra y Libertad periodical, and fought on the Catalan front.

As the war approached its end in early 1939, when Franco's Nationalists retook Catalonia, Paz and hundreds of thousands of anarchists sought asylum in France.

Over the next decade, Paz wrote multiple history books, including a biography of CNT figure Buenaventura Durruti, known as the most comprehensive account as of the late 2000s.

In the mid-1990s, Paz toured Italian public meetings following interest in Ken Loach's 1995 film about the Spanish Civil War, Land and Freedom.