 He served as priest in the Roman Catholic Diocese of Masaka until 15 December 1988.Ssentongo was appointed Auxiliary Bishop of Masaka and Titular Bishop of Pupiana on 15 December 1988.He was consecrated a bishop on 18 March 1989, by Bishop Adrian Kivumbi Ddungu†, Bishop of Masaka assisted by Archbishop Emmanuel Wamala, 
Coadjutor Archbishop of Kampala and Bishop Paul Lokiru Kalanda†, Bishop of Moroto.