Philip Sandeman Ziegler (born 24 December 1929) is a British biographer and historian.
Born in Ringwood, Hampshire, Ziegler was educated at St Cyprian's School, Eastbourne, and went with the school when it merged with Summer Fields School, Oxford. He attended Eton College and New College, Oxford, graduating with a degree in Jurisprudence with highest honours before joining the British Foreign Service. In the Foreign Service, he served in Laos, Pretoria and Bogotá, as well as with the Delegation to NATO in Paris.
In 1967 he retired from the Foreign Service, and joined the publishers Collins. Originally intending to be a novelist, he began a career as biographer with his life of Talleyrand's lover, the Duchess of Dino. He was editor in chief at Collins from 1979-80. He has written in various journals and newspapers including The Spectator, The Listener, The Times, The Daily Telegraph and History Today.
- Duchess of Dino (1962) on Princess Dorothea of Courland
- Addington: A Life of Henry Addington, First Viscount Sidmouth (1965)
- The Black Death (1969)
- King William IV (1971)
- Omdurman (1973)
- Melbourne : a Biography of William Lamb 2nd Viscount Melbourne (1976) on Lord Melbourne the Prime Minister
- Crown and People (1978)
- Diana Cooper (1981)
- Mountbatten. The Official Biography (1985)
- Elizabeth's Britain 1926 to 1986 (1986)
- Diaries of Lord Louis Mountbatten 1920–1922: Tours with the Prince of Wales (1987) editor
- Personal Diary of Admiral the Lord Louis Mountbatten, South-East Asia, 1943–1946 (1988)
- The Sixth Great Power: Barings 1762–1929 (1988)
- From Shore to Shore – The Final Years: The Diaries of Earl Mountbatten of Burma 1953–1979 (1989)
- Edward VIII, the Official Biography (1990)
- Brooks's: A Social History (1991) editor with Desmond Seward
- Wilson: The Authorised Life of Lord Wilson of Rievaulx (1993) on Harold Wilson
- London at War 1939–1945 (1995)
- Osbert Sitwell (1998)
- Britain Then and Now: The Francis Frith Collection (1999)
- Soldiers: Fighting Men's Lives, 1901–2001 (2001)
- Man Of Letters: The Extraordinary Life and Times of Literary Impresario Rupert Hart-Davis (2005)
- Legacy: Cecil Rhodes, The Rhodes Trust and Rhodes Scholarships (Yale University Press, New Haven & London, 2008)
- Edward Heath (Harper Press, 2010) ISBN 978-0-00-724740-0
- Olivier (MacLehose Press, 2013).