Porvoo cathedral (Finnish: Porvoon tuomiokirkko, Swedish: Borgå domkyrka) is a cathedral of the Evangelical Lutheran Church of Finland in Porvoo, Finland. It was built in the 15th century, although the oldest parts date from the 13th century. It is the seat of the Diocese of Borgå, Finland's Swedish-speaking diocese. The cathedral is also used for services by the Porvoo Finnish-speaking parish, which is administratively part of the Diocese of Helsinki. The church had first become a cathedral in 1723, when the diocese of Viipuri (Viborg) (now the Diocese of Tampere) moved to Porvoo, after the Russian occupation of Viipuri.
The church was originally made of wood. The first stone walls were built between 1410 and 1420, and in about 1450, the church was expanded four meters towards the east and six meters towards the south.
The church has been destroyed by fire numerous times; in 1508 by Danish forces and in 1571, 1590 and 1708 by Russian forces. On May 29, 2006, the outer roof collapsed after arson, however with the inner ceiling undamaged and the cathedral interiors intact. Kalle Holm, an eighteen-year-old black metal musician, was found guilty and convicted to three years and two months imprisonment on August 31, 2006. The Court of Appeal later increased the sentence to six years and six months on May 15, 2007. The Cathedral was reopened on July 2, 2008.
The Cathedral was the site of the opening of the first Diet of Finland on 28 March 1809, at which Finland was declared an autonomous Grand Duchy, with the Emperor of Russia as the Grand Duke of Finland.