Suomenlinna Church is one of the landmarks of the fortress. A functioning lighthouse and one of the most popular churches for weddings in Helsinki, Suomenlinna Church and its tower are an integral part of the skyline of southern Helsinki. The planning of the church began in 1748 when the fortress was established, but the first plans never came to fruition. At first, the military congregations worshipped in rooms not originally designed for religious use. When the fortress was transferred to Russia in 1808, it became home to an Orthodox community and an Orthodox church was set up in the Ehrensvärd Crownwork.

The construction of the current church started in 1849, and several wooden houses were demolished to make way for it. Designed by Konstantin Thon, the church was completed in 1854. The central tower of the church was surrounded by four smaller towers with onion domes. A fence was built around the church, made of cannon barrels and crossed chains.

In 1919, after Finland had gained independece, the Orthodox church was transformed into a Lutheran church. The iconostasis, movable effects and works of art were removed and the exteriors renovated for a simpler appearance. A lighthouse beacon was placed in the church tower to serve as a navigational aid for ships and air traffic. The beacon emits four consecutive flashes which in Morse code is the letter H, for Helsinki. The alteration work for the church included dismantling the main dome and four towers of the original church. The current church looks very different from the original. The church is still used by the Helsinki Cathedral Parish.