After graduating from
Somerville College,
University of Oxford in 1969, Bennett began her career in the Foreign Office in 1972 as a research assistant in what was then called the Historical Branch. She held a number of roles within the wider FCO, and in 1995 was appointed to the newly-created position of Chief Historian. In this role, she edited the documentary history of British foreign policy since 1945,
Documents on British Policy Overseas, and give historical advice to ministers and officials. In 1998, FCO historians were commissioned by
Foreign Secretary Robin Cook to investigate the authenticity of the
Zinoviev Letter, and Bennett authored the report of their findings, concluding that the letter was a forgery though not likely to have been directly the work of MI6 officers. In researching the origins of the letter, Bennett had full access to British government sources, and also drew upon Russian archival records. Bennett retired from the civil service in 2005, and was succeeded as chief historian by
Patrick Salmon. Since 2005, Bennett has published three monographs, ''Churchill's Man of Mystery: Desmond Morton and the World of Intelligence
(2006), Six Moments of Crisis: Inside British Foreign Policy
(2013), and The Zinoviev Letter: The Conspiracy that Never Dies'' (2018). == Major publications ==