He was one of the hereditary peers to have been excluded from the House of Lords. He inherited his peerage from his grandfather, Harold Macmillan, 1st Earl of Stockton, who was Prime Minister of the United Kingdom from 1957 to 1963. He was an unsuccessful candidate in the by-election in 2007 to replace Lord Mowbray in the House of Lords, coming third behind the winner, Earl Cathcart and Viscount Younger.
Both his father Maurice Macmillan (1921-1984) and his grandfather preceded him as Chairman of Macmillan Publishers Ltd., the publishing house long owned by the family. The 2nd Earl sold it to the German Holtzbrinck group. He ranked 127th in the Sunday Times Rich List 2004, with an estimated wealth of £326m.
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