Mériadec was a chaplain of the Empress Josephine de Beauharnais. He served as prior and doctor of the Sorbonne and provost of the church of Strasbourg before being crowned archbishop of Bordeaux on December 26, 1769. He remained there only a short time before leaving Bordeaux for the Cambric archbishop's palace, and died in Paris in 1813.
His mistress was Charlotte Stuart, Duchess of Albany, illegitimate daughter of Prince Charles Edward Stuart, with whom he had three children.