Louis-Ernest Dubois was born on September 1st 1856 in Saint-Calais. He was educated at the Seminary of Le Mans and ordained a priest on 20 September 1879. After his ordaination he worked in the diocese of Le Mans from 1879 until 1898. He was editor of Semaine du fidèle in 1888. He served as Vicar general of the diocese of Le Mans from 1898 until 1901.
Pope Leo XIII appointed him Bishop of Verdun on 18 April 1901. Verdun was one of only two French cities where the bishop was not obliged to leave his palace in 1905 during the separation of Church and state. He was promoted to the metropolitan see of Bourges in 1909 and then transferred to metropolitan see of Rouen on 13 March 1916.
He was created and proclaimed Cardinal-Priest of S. Maria in Aquiro in the consistory of December 4, 1916. He become Archbishop of Paris on 13 December 1920. He took part in the conclave of 1922 that electe Pope Pius XI. He remained as Archbishop of Paris until his death on September 23rd 1929. He is buried in Notre-Dame de Paris.