The most surprising aspect of this church is how early it reflected the latest trend in English church design and for a mostly Irish congregation. Resembling most closely A. W. N. Pugin's St. Oswald's Roman Catholic Church in Liverpool, England (1839–1842), St. Peter's represents Pugin's ideals that a church should function well without artificial symmetry and that the medieval period represented the perfection of church architecture. W. R. Crisp, a draftsman in Thomas Ustick Walter's Philadelphia office in the 1830s, supervised construction. Perched on a hillside above the Monongahela River, the square central tower has a spire rising ninety feet and visible for several miles. Referring to the rough-hewn stonework in praising St. Peter's “unostentatious charm,” architectural historian Talbot Hamlin wrote in Greek Revival Architecture in America (1944), “Hardly anywhere else have basically Gothic forms been so thoroughly Americanized.” The church represents one of the first tangible symbols of Catholicism in southwestern Pennsylvania. The single nave interior is simple, but appears richly ornamented from the rough-hewn stone to the exposed rafters. A carved stone spiral staircase leading to the choir loft and an exquisite baptismal font in the southwest corner are further evidence that a skilled practitioner was at work here. Stained glass windows represent the history of the Catholic Church since 1754.