Louis Marie Olivier Duchesne (; 13 September 1843 – 21 April 1922) was a French priest, philologist, teacher and a critical historian of Christianity and Roman Catholic liturgy and institutions.
Life
thumb|left|Duchesne in his presbyteral robe
Descended from a family of Breton sailors, he was born on 13 September 1843 in Saint-Servan, Ille-et-Vilaine, Place Roulais, now part of Saint-Malo on the Breton coast, and was orphaned in 1849, after the death of his father Jacques Duchesne. Louis' brother, Jean-Baptiste Duchesne, settled in Oregon City, Oregon in 1849.
thumb|220px|Duchesne, standing at right, [[École française de Rome, c.1873–1876]]
Louis Duchesne was ordained to the priesthood in 1867. From 1873 to 1876, he was a student at the École française in Rome. He was an amateur archaeologist and organized expeditions from Rome to Mount Athos, to Syria, and Asia Minor, from which he gained an interest in the early history of the Roman Catholic Church.
In 1877, he obtained the chair of ecclesiastical history of the Catholic Institute, but left the theological faculty in 1883. He then taught at the École Pratique des Hautes Études, where he influenced Alfred Firmin Loisy, a founder of the movement of Modernism, which was formally condemned under Pope Pius X. In 1895, he was appointed director of the École française.
In 1888, he became a member of the Académie des inscriptions et belles-lettres, and in 1910, he was elected to the Académie française. Abbe Duchesne was made an apostolic prothonotary in 1900.
As editor of the Bulletin critique du littérature, d'histoire et de théologie, Duchesne kept up with current intellectual developments.
He also wrote Les Sources du martyrologe hyéronimien, Origines du culte chrétien (translated as Christian Worship: Its Origin and Evolution and often reprinted),