The Reformed Church inside the Târgu Mureş fortress was built in the 14th century and include the former Franciscan convent, the chapel and the bell tower. A document issued by Pope Boniface II, of 23 November 1400, refers to the great altar of the Franciscan church.
Basically, there were three construction phases: during the first, between 1350-1370, were built the chapel and monastery, with stone moldings and other decorations similar to the former "St. Maria" church in Sibiu; between 1370-1400 was built the altar; finally, between 1400-1430 was built the church nave and between 1430-1450 the church tower.
The Gothic windows of the church had to be made later (1450-1460), with the support of John Hunyadi, who in 1442 made gifts for decorating the church. The two Flamboyant windows were made during Ştefan Báthory's reign. Sculptural works were made by stone mason Gheorghe (Gergius lapicide), which received 11 florins for his work.
The former Franciscan monastery was secularized by the Diet of Cluj (November 25 - December 7, 1556), and there was established the first laic school, Schola Particula. Here, after the reformed priest Gábor Nemes, was built a temple of worship for Romanian prince Michael the Brave.
In 1601 and 1602 the church was destroyed, and repaired in 1662 by Prince Michael Apofi I, then, in 1693, with the support of Chancellor Michael Teleki the church receives a wooden ceiling and a nearly flat roof, noted for his engravings made by Konrad von Weiss in 1736. In 1785 the architect Anton Tirck (Türck) transforms the church, which gains baroque forms.