Durning was ordained to the priesthood on the 23rd of June 1949 and in Philadelphia (USA). In September 1950 Bishop Dennis Vicent Durning C.S.Sp (by then Father) arrived by ship through the port of Mombasa to the District of Kilimanjaro where he was assigned as assistant Parish Priest in Mashati Parish (1950 - 1954), and from 1954 to 1956 he was pastor in the same parish.
In 1963 Rome created the new Diocese of Arusha and nominated Father Durning to be its founding Bishop.
Bishop Durning started shepherding the enourmous diocese of Arusha, starting with only four (4) established parishes namely; Arusha, Usa River, Monduli and Loliondo. He started with one diocesan Priest, the late Fr. Simon Sirikwa, twelve Holy Ghost Frs. and four (4) Precious Blood Sisters.
Bishop Durning served the Arusha Catholic Diocese (now Archdiocese) for 26 years before retiring officially in 1989, and went to work as pastor of Bashay Lambo in Mbulu Diocese where he ministred the family of God until his death on Feb. 21st. 2002 in KCMC hospital Moshi. He was burried in the Holy Ghost Parish Church of Ngarenaro. His body will be removed to the Cathedral, which is currently under construction at St. Theresa Parish.