Pierre was born in the east end of Montreal. He was a journalist and writer of militantly polemical essays and books in support of Quebec independence.
In 1966 he became the ideological leader of the FLQ terrorist organization and conducted a hunger strike at the UN headquarters in New York City to protest what he considered to be Quebec's plight. While there, he was arrested and convicted of manslaughter (but later acquitted in a second trial in 1970).
During his four years' imprisonment in New York, he wrote a number of works, the most famous (or perhaps notorious) of which was Nègres blancs d'Amérique (White Niggers of America). This book compared the situation of Québécois to that of African-Americans at the height of the latter's civil rights struggles. He also called for armed struggle.
Pierre returned to Montreal not long after the events of the October Crisis and renounced violence as a means to achieve Quebec independence, resuming his career as a journalist, writer, and publisher. He was also gay and spent his last few years living in Montreal's gay district.
He died of heart failure.