Built in the mid-thirteenth century, the temple is in the Gothic style, with a richly decorated, baroque interior. It still performs a sacred function, being at the same time a valuable monument of Kalisz. The church was elevated to the rank of a cathedral by Pope John Paul II in 1992. In 2016, the relics of St. Faustina Kowalska.
The construction of the church funded by prince Bolesław the Pious was completed in 1257. As a result of fires, the temple was rebuilt many times. Some of the decorations - patriotic polychromes and stained glass - are the work of a Young Poland artist - Włodzimierz Tetmajer. The history of the building is associated with many important figures from the history of Poland. In the church of St. Mikołaj, the poet Adam Asnyk was baptized, and the writer Maria Konopnicka was married. Both events are commemorated with stone tablets.
Until the seventies of the twentieth century, Rubens' painting "The Descent from the Cross" was displayed in the temple. However, it was stolen and its fate remains unknown.