Jerome Theisen was born in Loyal, Wisconsin, United States, on 30 December 1930, the ninth of ten children (five boys and five girls).

He came to Saint John's to initially study Latin in preparation for seminary, but was drawn to the monastic life and entered the abbey making his religious profession on 11 July 1952.

Theisen returned to America and began an extensive scholarly life writing books and articles, along with giving retreats, workshops, lectures, and serving as a professor at numerous academic institutions.

[1] As noted in his obituary: Father Jerome served as chaplain of the College and Convent of Saint Benedict, St. Joseph, MN; as associate director of the Institute for Ecumenical and Cultural Research; as an official Vatican visitator of seminaries; as a member of the Formation Committee of the Conference of Major Superiors of Men; and as Novice Master of Saint John's Abbey for a three-year term.

After only three years into his six-year term as Abbot Primate, Theisen died of a heart attack on 11 September 1995 and is buried at Saint John's Abbey in Collegeville, Minnesota.