In the past, this church was a wooden church, that Normans burnt and damaged few years later! It was located outside the city's surrounding walls, where markets and fairs took place.
That's why it was called Saint-Jean-du-Marché, "Saint-John of the Market"! First, it was dedicated to Saint John the Evangelist, then after the fire of 1524, to Saint John the Baptist, when the church was the property of the abbey of Notre-Dame-des-Nonnains.
The reconstruction dates back to the 13th century. At the end of the 14th century, the bigger part of the church was finished. But the building works went on for 150 years! They raised the bell-tower just before the terrible fire of 1524, which destroyed the nave and the lateral chapels. 30 years later, the church was restored.
By the way, did you know in the church, Henri V of England married Catherine of Valois, king of France Charles V's daughter in 1420? A wedding concluded with the famous treaty of Troyes, a treaty specifying that when king Charles VI the Mad will die, the king of England will be crowned king of France!
Henri left is crown and his brocade coat to the church, as a souvenir. They added a golden crown at the top of the bell-tower, which disappeared during the French Revolution...