John DeCoste was born in Arichat, Cape Breton, on June 2, 1943. He completed his primary and secondary school education in the village school under the guidance of the Congregation of Les Filles de Jesus. He went on to become a teacher in Halifax, Nova Scotia, and Cape Breton. In his third year of teaching, he decided to become a missionary priest in the community of the Missionaries of Africa (White Fathers of Africa). He was ordained to the missionary priesthood on August 23, 1975. He spent fifteen years in the African missions and was a witness to the Rwandan genocide and war. He was a chaplain for thirteen years in the Spiritual Care Department of the Ottawa Hospital, after which he semiretired from hospital work and returned to his Nova Scotia home. He is presently assistant chaplain at St. Ignatius Parish in Bedford, Nova Scotia.