Hugh Pattison Macmillan, Baron Macmillan GCVO PC QC (20 February 1873 – 5 September 1952) was a Scottish advocate, judge, Parliamentarian and civil servant.
The son of the Rev Hugh Macmillan (1833-1903) and Jane Patison (1833-1922), he was educated at Collegiate School, Greenock, at the University of Edinburgh (M.A. 1st in class honours in philosophy, 1893 Bruce of Grangehill and Falkland Scholarship) and the University of Glasgow (LLB). He was indentured for three years to the firm Cowan, Fraser and Clapperton while he studied the Law, in which he distinguished himself by winning the Cunningham Scholarship for Conveyancing in the year 1896. He was admitted to the Faculty of Advocates in 1897 with public defence of assigned Thesis on De diversis regulis juris antiqui, and later became King's Counsel in 1912. He wrote for a time articles in conveyancing for Green's Encyclopedia of Scots Law, and was Editor of the quarterly Juridical Review between 1900 and 1907.
Macmillan suffered an illness, and surgery thereon, in 1917, at which time he decided to cease his nascent political career (then in abeyance for the duration of the Great War). In October 1922, he was asked by Bonar Law to become the Solicitor-General for Scotland, which he declined because of his political stripe.
When the Labour government of Ramsay MacDonald was elected in 1924 - the first time the Labour Party had taken power - it had no KCs in Scotland amongst its Parliamentary representation. Macdonald therefore turned to Macmillan, whose reputation at the Bar was considerable, to take the job of Lord Advocate, even though he was a Conservative. He served as Lord Advocate from February to November 1924, and was sworn to the Privy Council on 16 April that year.