Saint Trésain (French pronunciation: [tʁe.zɛ̃]; or Tressan, Tresanus; 6th century) was an Irish missionary in France.

Saint Trésain is patron of Mareuil sur Marne (Mareuil-sur-Ay) and of the parish church of Avenay-Val-d'Or.

[1] The monks of St Augustine's Abbey, Ramsgate wrote in their Book of Saints (1921), Tresain (St.) (Feb. 7)(6th cent.)

[2] The hagiographer Alban Butler (1710–1773) wrote in his Lives of the Fathers, Martyrs, and Other Principal Saints under February 7, St. Tresain, or Tresanus, Priest and Confessor He was a holy Irish priest, who having left his own country, preached with great zeal in France, and died curate of Mareuil upon the Marne, in the sixth century.

He wrote that Trésain was born in Ireland of honest and prosperous parents and decided to dedicate himself to God.