The church was raised between 1820 and 1825 following the cathedral design of Piotr Aigner, and according to the plans of moving the bishop's headquarters to Suwałki. The main altar of a classicistical style (mid 19th century) situated on a high plinth in the church is the main place in the temple. In the middle of it there is the painting of Immaculate Mother Maria (by Anna Czartoryska, the 19th century). The second painting - of St. Alexander (a pope and a martyr) is situated behind the plinth hanging on the lines in the altar. It was painted in a romantic style in the first half of the 19th century (the author unknown) and it presents St. Alexander on the cloud with his hands being risen. In his right hand he is holding a martyrdom palm. At his feet there are a tiara and a pope crosier. The bottom of the painting presents a martyr scene.