[2] He was ordained a priest on 1 June 1985 for the diocese of Łomża by the diocesan bishop Juliusz Paetz.

[4] During his studies in Italy, Stepnowski served as a part-time pastor for the Roman Catholic Diocese of Terni.

First he dealt with some Spanish-speaking countries in South America, then for many years he headed the Office for Coordination of Visits "ad limina Apostolorum".

[4] On 11 November 2011 Stepnowski was appointed as the new bishop of the Łomża by Pope Benedict XVI.

[1] He adopted the phrase "Gratia et Pax" (Grace and Peace) as his bishop's motto.