The red sandstone façade of St. Ignatius rises above the low old town houses on Kapuzinerstraße. It is adorned with gray sandstone figures, including that of the church's patron saint and martyr, St. Ignatius of Antioch (+ after 110). The church was built between 1763 and 1774 according to plans by Johann Peter Jäger, replacing the old church in a suburb that was incorporated into the Mainz city wall after 1200.

The church displays an impressive interplay of Baroque, as an expression of religious joy, and Classicism, as an expression of reason. Lavish stucco work and cherubs appear between the strict lines of Classicism. Ceiling paintings tell the story of the life and death of St. Ignatius. They were originally created by the Baroque painter Johann Baptist Enderle, but were later reworked several times.

The classicist organ case (1774-81) above the main entrance is well worth seeing; the organ itself dates from 1837.

Beneath the church is a crypt where clergy and parishioners are laid to rest, along with the church's architect, plasterer, and carpenter. The towerless church is surrounded by a parish garden featuring a large crucifixion group, the tomb of sculptor Hans Backoffen (d. 1519), and a Gothic wooden crucifix.