Medardus or Medard (French: Médard or Méard) (ca. 456–545) was the Bishop of Noyon. He moved the seat of the diocese from Vermand to Noviomagus Veromanduorum (modern Noyon) in northern France. Medardus was one of the most honored bishops of his time, often depicted laughing, with his mouth wide open, and therefore he was invoked against toothache.

Medardus was born around 456 at Salency, Oise, in Picardy. His father, Nectaridus, was a noble of Frankish origin, while his mother Protagia was Gallo-Roman. The Roman Martyrology includes the fanciful tale that Gildard, Bishop of Rouen, was his brother, '"born on the same day, consecrated bishops on the same day, and on the same day withdrawn from this life." However, there is no mention of Gildard in the earliest lives of Medardus, and Gildard attended the First Council of Orléans in 511, while Medardus was not consecrated until 530.

A pious fiction links his childhood to his future bishoprics: "He often accompanied his father on business to Vermand and Tornacum (modern Tournai), where he frequented the schools, carefully avoiding all worldly dissipation".

Medardus lived during the immediate aftermath of the fall of the Western Roman Empire. The last Western Roman emperor was deposed in 476. During 481–511, the Salian Frankish king Clovis I conquered and united several Germanic successor states to form the Kingdom of Francia, the predecessor of modern France and Germany.

St. Medardus was ordained at the age of 33. His piety and knowledge, considerable for that time, caused Bishop Alomer of Vermand to confer on him Holy Orders. At the death of Alomer in 530, Medardus was chosen to succeed him as bishop of Vermand. Despite his objections, but the people insisted, so he accepted the responsibilities.

It is also claimed that in 532, at the death of Eleutherius, bishop of Tornacum, Medardus was invited to assume the direction of that diocese also. He refused at first, but being urged by Clotaire himself, he at last accepted. The union of the two dioceses of Noviomagus/Noyon and Tornacum/Tournai lasted until 1146, when they were again separated. Tornacum was a center for evangelizing the pagan Flemings. There, Medardus accepted Radegund of Thuringia as a deaconess and nun, until she moved to her own foundation at Saix.

King Clotaire, who had paid Medardus a last visit at Noviomagus, where the bishop died, had his body transferred to his own manor of Croviacum (modern Crouy), at the gates of the royal city of Noviodunum; there over his tomb was erected the celebrated Benedictine abbey which bears his name, the Abbey of Saint-Médard. The selection of the site was given authenticity through a familiar trope of hagiography:

Medardus was one of the most honored bishops of his time. His memory has always been popularly venerated, first in the north of France, then in Cologne and extending to western Germany, and he became the hero of numerous legends. His cultus is mentioned by both Venantius Fortunatus and Gregory of Tours. His feast day is celebrated on June 8. It is believed that, as with Swithun, whatever the weather on his feast day, it will continue for the forty days following, unless the weather changes on the feast of Saint Barnabas (11 June).