Professional life
Manningham-Buller worked as a teacher for three years at Queen's Gate School, Kensington, London from 1971 to 1974, having read English at Lady Margaret Hall, Oxford, before joining the Security Service. She was recruited to the Security Service at a drinks party when someone suggested that she see someone at the Ministry of Defence. Specializing in counter-terrorism rather than MI5's then-classical counter-espionage, she was active at the time of the Lockerbie bombing by Libya in 1988. During the early 1980s she was reportedly one of only five people aware that Oleg Gordievsky, the deputy head of the KGB rezidentura at the Soviet embassy in London, was a double agent. She was one of the few people who knew that it was Gordievsky who had exposed Michael Bettaney.
She was a senior liaison officer working out of Washington, D.C. to the US intelligence community over the period of the first Gulf War, before leading the newly created Irish counter-terrorism section from 1992 when MI5 were given the lead responsibility for such work (from the Metropolitan Police). Having been promoted to the management board of the Security Service the next year, Manningham-Buller became the director in charge of surveillance and technical operations. She was appointed Deputy Director General in 1997, and succeeded Sir Stephen Lander as Director General in 2002, the second woman to take on the role after Dame Stella Rimington.
In the 2005 Birthday Honours, Manningham-Buller was appointed a Dame Commander of the Order of the Bath (DCB). She resigned from MI5 on 21 April 2007, and was succeeded by her deputy, Jonathan Evans. She was raised to the peerage as Baroness Manningham-Buller, of Northampton in the County of Northamptonshire on 2 June 2008.
She reportedly joined the public speaking circuit. She was appointed to the Court and Council of Imperial College London in 2009, becoming deputy chairman later that year, and named chairman in July 2011. She became a governor of biomedical research charity the Wellcome Trust in 2008 and the first female chair of the Trust on 1 October 2015. She left the Wellcome Trust in 2021, being replaced as chair by Julia Gillard on 12 April 2021. From 2015 to 2025, she was co-president of Chatham House.
On St George's Day (23 April), 2014, Manningham-Buller was appointed a Lady Companion of the Order of the Garter (LG) by Queen Elizabeth II.
She became chair of the Conduct Committee on 19 January 2022. She took part in the Royal Procession at the Coronation of Charles III and Camilla, carrying St Edward's Staff.