Also known as the Mission Church, this Romanesque Revival landmark gave Mission Hill its name. Built by the Redemptorist Fathers with no defined parish, it originally served all who wished to attend. The Redemptorists were largely a German Catholic order, and Parker Hill—now called Mission Hill—had a large German American population. The German connection explains why two New York architects, William Schickel and Isaac Ditmars, were selected. Schickel was born in Germany and trained in the office of Richard Morris Hunt. Ditmars was from Nova Scotia. Although collaborating in this design, the two men apparently did not work as a partnership until later in their careers.
The church is constructed of locally quarried Roxbury puddingstone contrasted with granite and sandstone. The exterior stylistic elements are primarily Gothic; one obscure reference suggests that Edward W. Pugin, son of famed English Gothic Revival architect Augustus W. Pugin, provided a preliminary design for the church.
An octagonal lantern crowns the transept of the basilica plan. Untersee added the towers in 1910. He also designed the rectory in 1903, a building whose contrasting colors of pressed brick and limestone trim prevent its being visually over-shadowed by the church. Untersee also designed the puddingstone Romanesque Revival St. Alphonsus Hall (1898), directly behind the cathedral, the center of three church buildings (flanked by a grammar school and convent) on Smith Street proposed for demolition and replacement by market-rate housing.