Martial-Guillaume-Marie Testard du Cosquer (September 22, 1820 – July 27, 1869) was a French prelate of the Catholic Church who served as the first Archbishop of Port-au-Prince (1863-1869).

[1] After graduating from the royal college of Pontivy in 1838, he studied at the Faculty of Law of Paris and earned a doctorate in 1841.

[3] While in Rome, he served as a chaplain to the French troops under General Charles Oudinot during the 1849 siege of the city and was subsequently awarded the Legion of Honour.

He received his episcopal consecration in Rome on the following October 18 from Cardinal Costantino Patrizi Naro, with Bishop Carlo Belgrado and Archbishop Alessandro Franchi serving as co-consecrators.

[3] Upon his return to Haiti on June 10, 1864, du Cosquer received a warm welcome and visited President Fabre Geffrard, to whom he presented the insignia of the Order of St. Gregory the Great as a gift from Pope Pius IX.