The people of Savonlinna had to go to the Sääminki church when they didn't have their own church. In 1850 governor Aleksander Thesleff gave order to build a church in Savonniemi. The actual construction began in 1874 and was completed in 1878. The church was designed by architect Axel Hampus Dahlström in the Gothic Revival style and it has room for 1000 people.
In 1896 the new diocese of Savonlinna was founded and the Savonlinna church became a cathedral. The first bishop was Gustaf Johansson. In 1925 the bishop's seat was moved to Vyborg, but the church still retained "cathedral" as its name.
During the Winter War in 1 May 1940 Savonlinna was bombed and the church was damaged. It was restored in 1947–1948 by architect Bertel Liljeqvist. In 1990–1991 it was renovated by Ansu Ånström.
The Church of St Donatus name refers to Donatus of Zadar, who began construction on this church in the 9th century and ended it on the northeastern part of the Roman forum. It is the largest Pre-Romanesque building in Croatia.
The beginning of the building of the church was placed to the second half of the 8th century, and it is supposed to have been completed in the 9th century. The Zadar bishop and diplomat Donat (8th and 9th centuries) is credited with the building of the church. He led the representations of the Dalmatian cities to Constantinople and Charles the Great, which is why this church bears slight resemblance to Charlemagne's court chapels, especially the one in Aachen, and also to the Basilica of San Vitale in Ravenna. It belongs to the Pre-Romanesque architectural period.
The circular church, formerly domed, is 27 m high and is characterised by simplicity and technical primitivism.