His experience of this total war profoundly affected MacLeod, leading him to train for the ministry. He studied divinity at the University of Edinburgh, followed by a year at Union Theological Seminary, New York City. Upon return to Scotland he was invited to become Assistant at St Giles' Cathedral. During this period he became increasingly concerned over the issue of social inequality in Scotland. In 1924 he was ordained as a Church of Scotland minister, to be Padre of Toc H in Scotland. Such non-parochial appointments were extremely unusual at the time. Following a disagreement, he resigned from Toc H in 1926, but was invited to become associate minister at St Cuthbert's Church, Edinburgh. His wartime experiences, combined with a profound disillusionment by post-World War I political rhetoric of "a land fit for heroes," deeply affected him. Confronted by the realities of the depression and unemployment faced by those less privileged than he, MacLeod gradually moved towards supporting socialism and pacifism. From 1937 he became actively involved with the Peace Pledge Union, and from 1958 with the Campaign for Nuclear Disarmament. Meanwhile, in 1930, to considerable surprise, he decided to leave St Cuthbert's Church to become minister at Govan Old Parish Church—encountering the considerable social problems caused by poverty in this part of Glasgow. The pace of work took its toll and in 1932 he suffered a breakdown. He spent some time recuperating in Jerusalem in early 1933. While worshipping in an Eastern Orthodox Church on Easter Day he felt a profound spiritual experience, feeling a sense of recovery of the Church as the corporate Body of Christ. This would strongly influence the rest of his life. He resigned to become the full-time leader of the Iona Community, which he founded in 1938. His efforts started in the early 1930s when he bought Fingleton Mill as a refuge for Glasgow's poor. The idea of rebuilding Iona Abbey using ministers, students and unemployed labourers working together influenced his thinking; the Iona Community developed as an international ecumenical community, with offices in Govan and a presence on the island of Iona. Underpinning the fellowship of the Community were four emphases: mission, political involvement, a ministry of healing, and worship, by which MacLeod and the Community sought a way to connect the Church with an industrial age. He led a series of parish missions in Scottish parishes associated with the Community, and supported the 1950 Glasgow Churches' Campaign and the 1950s Tell Scotland Movement. However, he opposed the invitation promoted by Rev. Tom Allan to Dr Billy Graham that led to the 1955 All-Scotland Crusade.
Later life
During World War II, he served as locum minister at Canongate Kirk in Edinburgh—a parish also then afflicted by poverty. In 1948 he married Lorna; immediately after the wedding they travelled to Australia for a preaching tour. The 1940s and early 1950s were a difficult period professionally. MacLeod was involved in what became known as the "Govan Case." He was invited by the congregation to return to Govan Old Parish Church in 1948, but the Presbytery of Glasgow refused to approve his appointment, given his wish to continue his active leadership of the Iona Community. The case was referred to the General Assembly; ultimately he was refused permission to combine the two posts. Despite a feeling of hurt and rejection over the "Govan Case", MacLeod remained one of the highest-profile figures in the Church of Scotland. In 1957 he was elected Moderator of the General Assembly of the Church of Scotland, following one Commissioner standing up and asking whether it was appropriate that a man who had been described as being "half way to Rome and half way to Moscow" should be Moderator. In 1967 MacLeod was awarded a peerage, becoming Baron MacLeod of Fuinary, of Fuinary in Morven in the County of Argyll - the only Church of Scotland minister to have been thus honoured. He later became the first peer to represent the Green Party. George MacLeod's influence on the Church of Scotland was considerable. His initial emphasis on parish mission was generally welcomed and favourably compared to the campaigns of his contemporary, D.P. Thomson. Although dismissed by some as a maverick, he helped to raise awareness of pacificism, ecumenism and social justice issues, and inspired many to become involved with such questions. Through the creation of the Iona Community, he was a pioneer of new forms of ministry. In 1989 MacLeod received the Templeton Prize.