Pannella, whose real first name was Giacinto, was 86 and had been suffering from lung and liver cancer.
He was involved in campaigns on virtually every social issue of the post-war period, the most significant being the battles for divorce, which was legalised in 1970, and abortion, legalised in 1978.
The struggles pitted Pannella and like-minded people against the might of the Catholic church.
Pannella also campaigned against hunting and nuclear power, and for gay rights and the decriminalisation of soft drugs.