At the highest point of the medieval town center, at the Obermarkt, rises the "Oberkirche", as it has been called since time immemorial. The name "Eichsfeld Cathedral" is also widely used to express the fact that this church is one of the largest, most beautiful and most impressive in the Eichsfeld. Perhaps this name goes back to the 17th century, when Duderstadt was the seat of the ecclesiastical commissary (1636-1781) for the entire Eichsfeld region.

Alongside the town hall, the Catholic parish church is one of the oldest buildings in Duderstadt. Construction of the imposing westwork began as early as 1250. The broad base of the twin towers with its wimpergen (pointed gables) and the magnificent portal, which resembles the west portal of St. Elisabeth's Church in Marburg, are unmistakable features of the early Gothic period. Originally, the church only had the northern tower, 62.50 m high, from which the town watchman could overlook the surrounding hill forts. According to the ground plan of the westwork, the southern tower was originally planned, but for unknown reasons was not built in the Middle Ages. It actually owes its present existence to the fire of 1852, which destroyed the church roof and the top of the northern tower. When work began to repair the old tower, its right-hand brother was finally added after more than 600 years. Since then, the gilded spire finials, one of which bears a cross and the other a cockerel as a weather vane, have shone out over the countryside from a height of 65 meters.

The interior of the church has late Gothic features. The central nave is closed off by a net vault with 52 keystones. The furnishings are rich and very valuable. Winged altar (around 1500), Holy Kinship (16th century), Baroque baptismal font (1694) and oversized pillar figures, Romanesque reliquary cross from the Ottonian period, guild chandelier (18th century) and the Gothic pulpit. There is also an important baroque organ, which was built between 1733 and 1735 by master organ builder Joh. Creutzburg from Wendehausen (Eichsfeld) and restored in 2006 by the Eule workshop in Bautzen.