Claude Vivier (14 April 1948 – 7 March 1983) was a Canadian composer.
Born to unknown parents in Montreal, Vivier was adopted at the age of three[1] by a poor French-Canadian family. From the age of thirteen, he attended boarding schools run by the Marist Brothers, a religious order that prepared young boys for a vocation in the priesthood. At the age of eighteen, Vivier was asked to leave the novitiate.[2] His earliest works date from this period. He was always open about his homosexuality.

In 1971, following study with Gilles Tremblay, he began a period of three years' study in Europe, first with Gottfried Michael Koenig at the Institute for Sonology in Utrecht, and then in Cologne with Karlheinz Stockhausen. Vivier learned much from Stockhausen, and his early works have aspects that are clearly, and sometimes audibly, derivative of his teacher, even though his later works bear little audible resemblance.[3] In 1974, he returned to Montreal and began to establish his reputation. He spent some years travelling in places such as Japan, Bali and Iran.

Vivier's opera Kopernikus, to his own libretto, was premièred on 8 May 1980, at the Monument-National in Montreal.

Vivier returned to Paris. He was murdered on 7 March 1983 by a 19-year-old male prostitute he had met that evening at a bar. His body was discovered five days later, on 12 March.