In 1968, he joined the Communist Party of Spain and was a close friend of Santiago Carrillo.
He was arrested on several occasions and viciously persecuted by the Political-Social Brigade, the political secret police of the Franco regime.
[2][3] He left the CPS in 1988 and joined the Spanish Socialist Workers' Party (PSOE) two years later.
[4][5] In the 1980s, Curiel was a regular contributor to the Spanish daily newspaper El País.
[7][8] In his obituary in El País, Rafael Fraguas described Curiel as "Handsome, cordial and affable, more pragmatic than doctrinaire, subtle agitator, endowed with a convincing logic and endowed with an evident charisma, his image was in open contrast with the stereotype of the Stalinist communist - bitter, sectarian and dogmatic - spread by Francoism.