He accompanied his father, a militant of the Basque Nationalist Party, to exile in Chile during the Spanish Civil War.
[1] After high school, he studied law in the United Kingdom, earning a doctorate in University of Cambridge, after which he returned to the Basque Country and embarked on nationalist political activity.
[2] He was one of the founders of "Ekin" in the early 1950s, a splinter organization of the Basque Nationalist Party youth that was the embryo of the future Euskadi Ta Askatasuna (ETA).
He was a leader of ETA, a prominent member of Herri Batasuna and, later, founder of the political party Aralar and was close to the pacifist organization, Elkarri.
Madariaga served long prison sentences and spent years in exile, but severed his links with ETA in 1989 after becoming disillusioned with the group's methods.