Monsignor Michel-Gaspard Coppenrath was born on June 4, 1924, in Papeete, and was ordained to the priesthood at the age of 30, in Poitiers, France, on June 29, 1954. With a civil law degree and a doctorate degree in canon law, he served from vicar in Papeete to parish priest in Tahiti's North Coast commune of Pirae, dealing particularly with the media and youth movements.

He became vicar general to Msgr. Paul Mazé in 1966, and was appointed as Coadjutor of the Archdiocese of Papeete, French Polynesia, on February 16, 1968, at the age of 43, receiving his episcopal consecration with the titular archbishopric see of Tigisi in Numidia on the following June 3, from Archbishop Paul-Laurent-Jean-Louis Mazé SS.CC., assited by Archbishop Pierre-Paul-Émile Martin SM., and Bishop Louis-Bertrand Tirilly SS.CC.

Msgr. Coppenrath succeeded to the Metropolitan See of Papeete on March 5, 1973. When he retired from active duty on June 4, 1999, the Holy See, appointed his younger brother, Hubert Coppenrath, as Papeete's third archbishop, being considered thus, a rare event for the Church, with the passing on of such an important post to a brother.

The Archbishop died of ruptured aneurysm on Saturday, August 16, 2008, aged 84. Wake took place on the following evening, starting at seven in the evening at the Maria no te Hau church in Papeete's mission neighborhood. Funeral and burial services were held on Monday, August 18, presided by his brother, Archbishop Hubert. Out of respect, all Catholic schools in Tahiti's communes of Faa'a, Papeete, Pirae and Punaauia were closed all day on the day of his funeral. Thousands participated in his funeral, including French state and French Polynesia government officials.