Hydrographer at the French naval ministry’s depôt des cartes (1772). Discovered and calculated orbits of numerous comets. Elected to the Académie des sciences (1782). Editor of the French national almanac Connoissance des temps (1785). Commissioner in Anglo-French project to triangulate Greenwich and Paris observatories (1787). Appointed to calculate geodetic measurements of southern France based on the new unit of length, the meter (1790). Suffered professional setbacks in French revolution but ultimately appointed director of Paris observatory.
Son of Pierre-François and Marie- Marguerite (Roze) Méchain. Educated at École des Ponts et Chaussées at Paris but did not complete course. Married Thérèse Marjou (1777); three children.