Cavendish was born in London, but raised in Switzerland and grew up speaking English, German, Swiss-German and French. He volunteered for the British Army in 1944 and served in Secret Intelligence Middle East (SIME) where he struck up a lifelong friendship with Maurice Oldfield, a future Chief of the Secret Intelligence Service. Following his demobilisation in 1948, he was recruited as the Secret Intelligence Service's youngest officer, aged 21, and worked in R5, the counterespionage section.
Cavendish left MI6 in 1953 and turned to journalism, covering Eastern Europe and the Middle East for United Press International and filing acclaimed eyewitness dispatches from Budapest during the Hungarian Revolution of 1956. He subsequently pursued a career as a businessman and merchant banker, but remained friendly with former colleagues in the intelligence world.
When Oldfield fell victim to a smear campaign in 1980, following his appointment as British Prime minister Margaret Thatcher's security supremo for Northern Ireland, Cavendish defended him, taking on the Establishment and publishing a slim volume of memoirs called Inside Intelligence. This attempt to restore his old friend's reputation led to a two-year game of cat-and-mouse with Whitehall censors until the House of Lords threw out the government's case. The book was published formally by HarperCollins in 1990.
- "Flamboyant intelligence officer who was a drinking partner of Kim Philby and later wrote a controversial book about working for MI6". The Times. Retrieved 26 January 2013.
- "Anthony Cavendish: Intrepid intelligence officer who fought terrorism in the Middle East". London: The Independent. Retrieved 23 March 2013.
- Cavendish, Anthony (1997), Inside Intelligence, HarperCollins, London.
- Norton-Taylor, Richard (23 January 2013). "Former MI6 officer who chronicled his exploits as a secret agent in Inside Intelligence". London: The Guardian. Retrieved 26 January 2013.