A leading figure and renowned preacher in the world ecumenical movement. Born in Dominica of a Methodist mother and Roman Catholic father, he was found sitting on a barrel on a pier by the Rev. W. Arnold Beckett (1893-1976; e.m. 1927), who served for 27 years in the Leeward Islands. He trained for the Methodist ministry at Caenwood, Jamaica and Richmond College. As Secretary of the British SCM he led the youth delegation to the first World Council of Churches Assembly in 1948. After four years serving in Haiti, he was appointed to the Youth Department of the World Council of Churches in 1954. In 1960 he was elected President of the World Student Christian Federation and in 1961 became the first overseas minister to be a Secretary of the MMS, in succession to Tom Beetham. He was appointed Director of World Mission and Evangelism in the World Council of Churches in 1967 and served as General Secretary of the Council 1972-1984. He died in April 2015.
His first wife, Doreen Potter, a musician and composer, died in 1980. His widow, Barbel Wartenburg-Potter, is Bishop-Emeritus of the German Protestant Church.