For over four decades, Donnelly has served as a church choir and Schola director, and since 2021, he has been based in Omaha, Nebraska, where he directs the Domus Mariae Ensemble and teaches voice. He is the pioneer of “Organum Novi Mundi,” a compositional technique that renders Gregorian Chants in the classical harmonic style of the west, while preserving the Chant’s liturgical integrity. His compositions, including the Missa Sicut Cervus and numerous Latin motets and hymns, are created with the purpose of bringing souls closer to God. In addition to his work as a composer, Donnelly is a vocal clinician for various choirs, including the monks at Clear Creek Abbey, and hosts the podcast “ChantHacks,” which shares practical techniques for singing Gregorian Chant.