Sir Anthony Arthur Duncan Montague Browne KCMG CBE DFC (8 May 1923 – 1 April 2013) was a British diplomat who was private secretary to Sir Winston Churchill during the last ten years of the latter's life.

Montague Browne was the biological father of Justin Welby, the 105th Archbishop of Canterbury, but Welby learned that only after paternity testing had been taken after Montague Browne's death.

Montague Browne was the son of Andrew Duncan Montague Browne (1878–1969), a British army colonel, by his marriage to Violet Evelyn Downes (1883–1969). He was educated in Switzerland and then at Stowe School, where he refused to join the Officers' Training Corps until World War II had broken out in September 1939.

In September 1941, Montague Browne went up to Magdalen College, Oxford, but left in spring 1942 to join the Royal Air Force. After learning to fly in a de Havilland Tiger Moth with No. 9 Elementary Flying Training School at RAF Ansty near Coventry, he was sent to train in the United States via Canada. He graduated as a fighter pilot with the US Navy pilots school and returned to the UK to train to fly the Bristol Beaufighter with the RAF. After assignment to squadrons flying in Egypt, Palestine and Cyprus, he was assigned to 211 Squadron RAF at Chiringa in Arakan, on the Burma-Bengal border. In 1945 he was awarded the Distinguished Flying Cross for his skill and valour attacking Imperial Japanese Army lines of communication within occupied Burma. In May 1945, he was promoted a flight lieutenant.

After returning to Magdalen College, Oxford, for a year, Montague Browne entered the Foreign Office in 1946. His first post was as private secretary to the then Permanent Under-Secretary of State for Foreign Affairs, Sir Orme "Moley" Sargent. After a period as the Foreign Office resident clerk (the political night duty officer), he was assigned to the Western Union Secretariat, which led the UK drafting of the North Atlantic Treaty.

In November 1949 he was posted to the British Embassy in Paris, France, partly because of his knowledge of French, which was developed during his schooling in Switzerland. Montague Browne was second secretary in the Chancery (political section), responsible for monitoring North Africa, covering Egypt to Tangier. With the French sceptical of Anglo-American intentions in North Africa and French internal politics then dominated with the rise in electoral power of the French Communist Party, Montague Browne was chosen by the British Ambassador to France, Sir Oliver Harvey, to do the internal political reporting of French concerns.

In September 1952, Montague Browne was chosen to be Private Secretary for Foreign Affairs to the Prime Minister, Winston Churchill. Until 1955, the role was undertaken jointly with Jock Colville. When Churchill retired in 1955, Montague Browne briefly returned to the Foreign Office but in the same year was seconded to continue as Churchill's private secretary. He stayed with Churchill for the rest of Churchill's life. At first, Churchill was doubtful of him and observed, "I dare say we will get on very well together". As well as his duties as a chief of staff, Montague Browne lunched and dined with Churchill and provided an opponent for his favourite card game, rubicon (six pack bezique). He also accompanied Churchill on his trips abroad. After Churchill's fall in Monaco in June 1962 when he broke his hip, Montague Browne arranged and accompanied him on the RAF flight back to London to assure, as Churchill wished, that if he died, he would die in England. In 1965, on Churchill's death on 24 January, Montague Brown witnessed Churchill's death certificate and liaised between his family and the government regarding Churchill's funeral arrangements.

After Churchill's death, Montague Browne was seconded to the Royal Household (1965–67). He then worked for companies in the City of London, including International Life Insurance and Gerrard and National. He also served as a trustee of the Winston Churchill Memorial Trust in the UK.