Over its long history this church has felt the hand of many architects and designers, resulting in a medley of styles, not all harmonious. Some of the remaining Romanesque sections date to the early 1200s. The exact date of the chancel is not known, but it's probably from the mid-14th century. The catacombs remain as they were in the Middle Ages.
Most of St. Michael's as it appears today dates from 1792, when the facade was redone in neoclassical style; the spire is from the 16th century. The main altar is richly decorated in baroque style, and the altarpiece, entitled The Collapse of the Angels (1781), was the last major baroque work completed in Vienna.