He entered the Society of Jesus on 30 Sept. 1869, and from 1884 to 1893 taught dogmatic theology to his German confreres in exile at Ditton-Hill (England), and from 1895 to 1912 to the same group, now transferred to Valkenburg; thereafter he devoted himself solely to his work as a writer.
In addition to extensive contributions to the cultural periodicals Stimmen aus Maria Laach, Stimmen der Zeit and Zeitschrift für katholische Theologie, he wrote: Praelectiones dogmaticae (9 vols., Freiburg im Br. 1895–99; 4th and 5th ed. 1925); also issued in a compendium for seminary use (4 vols., ibid. 1913–14). Special studies: Zur neuen Literatur über Nestorius (ib. 1914); De inspiratione S. Scripturae (ib. 1916; 2nd ed. ib. 1925; suppl. ib. 1926), notable especially for its positive section; Nestorius als Irrlehrer (Paderborn 1921); Die selige Jungfrau Maria, die Vermittlerin aller Gnaden (Freiburg im Br. 1923). From 1900 to 1916 he published a series of six studies on topical theological questions in the collection he founded, Theologische Zeitfragen; noteworthy are the 4th, Glaube, Dogmen und geschichtliche Tatsache (ib. 1908; Italian trans., Rome 1909), and the 5th, Glaubenspflicht und Glaubensschwierigkeiten (ib. 1908; Italian trans., Il dovere della fede, Rome 1911). Ascetical works include Die hl. Schutzengel (ib. 1917) and on the Sacred Heart, Unser bester Freund (ib. 1923).
Rich in patristic, historical and exegetical learning, and possessed of a remarkably balanced disputational spirit, his chief merit lies in having secured the substantial achievements of the positive critical method for the traditional structure of Scholasticism, drawing inspiration from St Thomas, de Lugo and Suárez. The Praelectiones dogmaticae remain to this day one of the most complete modern theological textbooks. In the modernist era, Fr Pesch played an effective and decisive part in eliminating it from Germany.