Ms Manningham-Buller has worked at MI5 since 1974
Eliza Manningham-Buller, is currently Deputy Director-General of the Security Service.
The former teacher is the second woman to be appointed head of the service.
She will take over from the current Director General, Sir Stephen Lander, in October.
Ms Manningham-Buller joined MI5 in 1974.
Her early work involved Soviet espionage and she worked on the case of Oleg Gordievsky - the former KGB defector.
She also worked for much of her time in counter-terrorism, both international and domestic.
The day after the 11 September attacks she flew out to Washington to liaise with the US authorities.
The first woman head of the Security Service was Stella Rimington, now Dame Stella Rimington.
She sparked a row after her departure with the publication of her autobiography, in which she called for the Official Secrets Act to be radically reformed.
Married
Critics argued she should never have been allowed to write a book about her work.
Ms Manningham-Buller has served as director for surveillance and technical operations and as director of Irish counter-terrorism.
She has been the deputy director general of the Security Service since 1997.
A woman who likes crosswords, she is married to husband David.