Haydon was born around 1917; no specific year is given but he is known to have been an undergraduate at Oxford University in 1937. He comes from an aristocratic family with connections throughout British high society. A polymath of sorts with a brilliant and charming personality, he excels as a student, takes up remote languages with ease, and proves a gifted painter while at Oxford. He is identified for recruitment in the Circus (John le Carré's lightly fictionalised version of MI6/SIS) by his tutor and acts in turn as a talent-spotter among his classmates, most noticeably Jim Prideaux with whom he forms an enduring friendship and possibly a homosexual relationship. In World War II, Haydon builds a superb record in Nazi-occupied Europe and the Middle East, such that he elicits comparisons with Lawrence of Arabia. Unbeknownst to the British, Haydon is also recruited as a Soviet agent around that time by Karla, Moscow Centre's crafty and legendary spymaster.
After the war, Haydon holds positions of increasing importance in the Circus, becomes its premier expert on the Soviet Union, and eventually rises to the senior staff of Control, the unnamed Chief of the Circus. In the early years of the Cold War, he limits his espionage activities to 'selected gifts of intelligence' that advance the Soviet cause over the American one without harming British interests. The Suez crisis of 1956 convinces him that Britain has lost all influence as a world power and leads him to become a 'full-fledged Soviet mole with no holds barred.' In 1961, he formally receives Soviet citizenship, then achieves the rank of Soviet intelligence colonel and is awarded further Soviet decorations over the next ten years.
Control has come to suspect that there is a mole deep in the organization. By 1972, alone in this belief, he has ruled out all but his five senior lieutenants: Percy Alleline, Roy Bland, George Smiley, Toby Esterhase, and Haydon. To save his agent, Karla engineers the demise of Control and Smiley whom he reckons to be the most likely to unmask Haydon. Karla is aware of Smiley's one personal weakness, his unreciprocated love for his wife Ann who is a habitual adulterer, and orders Haydon to have an affair with her to cloud Smiley's judgment further. As Control is about to discover the truth, Karla lures him into ordering a doomed operation in Czechoslovakia to learn the identity of the mole from a (fake) Czech defector. Control picks Jim Prideaux for the operation and Haydon has no choice but to sacrifice his close friend to save himself. Prideaux is captured and reveals under duress the full extent of Control's knowledge of the mole to Karla before being repatriated to Britain and discharged from the Circus. Control is dismissed and dies soon afterwards, Smiley is forced into retirement, and Alleline becomes Chief. Haydon assumes control of London Station which he maneuvers into being placed in control of all foreign stations, effectively giving him unfettered access to intelligence and details of operations worldwide.
In 1973, an indiscretion by a Soviet operative in Hong Kong confirms the existence of the mole to Oliver Lacon, the Civil Service overseer of the Circus in Whitehall. Smiley is recalled from retirement to investigate and ultimately unmasks Haydon after a tortuous, soul-searching quest. Under interrogation, Haydon reveals much of his secret past to Smiley and plans are set in motion to exchange Haydon for Western agents held in the Eastern Bloc but before this happens he is killed while still in Circus custody. It is strongly implied, though never stated, that the killer was Prideaux.
Haydon is portrayed rather in the mould of real-life double agent Kim Philby who is known to have compromised le Carré's own career in MI6; certainly his actions parallel Philby's ability to paralyse the British intelligence service. Haydon claims that, although he was recruited by Soviet intelligence at university in the 1930s, he only became a serious agent for them following the Suez crisis when it became clear to him that Britain was no longer a world power and, in his view, was subservient to America. This perceived inferiority led to Haydon developing a deep hatred for America and resolved him to damage them as much as possible by spying for the Russians.
Haydon was played by Ian Richardson in the 1979 BBC television serial based on the novel. In the 1988 BBC Radio 4 series, he was played by Edward de Souza. In the 2011 film adaptation, he was played by Colin Firth. In the 2011 Radio 4 series, The Complete Smiley, he was portrayed by Michael Feast.
- Palmer, Martyn (13 July 2011). "'Britain, like every nation, chooses for her spies people who are brilliant at complicity': Colin Firth on those leading a double life". MailOnline. Retrieved 15 April 2013.
- Brennan, Zoe (2 April 2011). "What does John Le Carre have to hide?". Daily Telegraph. Retrieved 15 April 2013.
- "Bill Haydon (Character)". IMdB. Retrieved 15 April 2013.
- Thulin, Anders. "Tinker Tailor Soldier Spy: Starring Bernard Hepton as George Smiley (BBC Radio Collection)". Amazon Reviews. Amazon. Retrieved 15 April 2013.
- Staff. "The Complete Smiley". iPlayer Radio. BBC. Retrieved 15 April 2013.
- le Carré, John (1974). Tinker, Tailor, Soldier, Spy. Hodder & Stoughton. ISBN 0-394-49219-6.
- "The Plot Spot plot summary: Tinker, Tailor, Soldier, Spy". The Plot Spot. Retrieved 15 April 2013.