In 1756, the monks proceeded with the last new construction of the church, which was completed in 1766. The well-known master builder Johann Kaspar Bagnato played a major role in the planning, while the construction supervision was in the hands of Johann Michael Beer. The builders were the abbots Cölestin Gugger von Staudach and Beda Angehrn. After the abolition of the monastery, the church became a cathedral (bishop's church) in 1824. It underwent an interior renovation from 1961 to 1967 and an exterior renovation from 2000 to 2003.

The church has an elongated, rectangular floor plan. The rotunda (round building) is inserted into it in the manner of a transept. On the eastern narrow side, the impressive two-tower façade rises as a dominant display front, the landmark of the diocese, city and canton of St. Gallen. The sculptural decoration of the façade includes the figures of St. Mauritius and Desiderius and the relief with the coronation of Mary by the Holy Trinity.

The interior of the church presents itself as a three-nave free pillar complex with a central dome (rotunda). High-quality stuccowork, vault paintings, altars and the choir stalls are among the highlights of the interior. The concept of harmoniously coordinated art forms originates from Christian Wentzinger, sculptor and painter.