Désiré-Félicien-François-Joseph Mercier (21 November 1851 – 23 January 1926) was a Belgian cardinal of the Roman Catholic Church and a noted scholar.
A Thomist scholar, he had several of his works translated into other European languages.
He was known for his book, Les origines de la psychologie contemporaine (1897).
His scholarship gained him recognition from the Pope and he was appointed as Archbishop of Mechelen, serving from 1906 until his death, and was elevated to the cardinalate in 1907.
Mercier is noted for his staunch resistance to the German occupation of 1914–1918 during the Great War.
After the invasion, he distributed a strong pastoral letter, Patriotism and Endurance, to be read in all his churches, urging the people to keep up their spirits.