Statesman. Born in Lady Road in the Craigmillar Park district of Edinburgh, the son of William Ivison Macadam, a chemistry lecturer who had met an untimely death in 1902. He was educated at Melville College and, after military service during the First World War, studied engineering at King's College London and Christ's College, Cambridge. At King's College, he was President of the student union, a building now known as the Macadam Building. He was involved in the formation of the National Union of Students, as the merger of the International Students Bureau Inter-Varsity Association and the and became their first President. Their national headquarters is now also named in his honour.
In 1929, he became the first Director-General of the Royal Institute of International Affairs, serving until 1955. Based at Chatham House, Macadam developed their reputation as an unbiased forum for the discussion of world affairs.
He died in London but was buried near his parents in Portobello Cemetery (Edinburgh). Amongst his many honours, he was awarded an OBE for his military service in 1919, a CBE in 1935, CVO in 1953 and knighted in 1955.