Born Marcia Field, Falkender was educated at the independent selective Northampton High School for Girls and read for a BA in History at Queen Mary College, University of London. After graduating she became secretary to the General Secretary of the Labour Party in 1955.
In 1956, Marcia Williams, as she was then known, became private secretary to Harold Wilson, Member of Parliament for Huyton, a position she retained until 1964, when she rose to be his political secretary and head of the political office in his position as leader of the Labour Party and as Prime Minister from 1964 until 1970 and again from 1974 to 1976. Falkender claims that she first met Wilson when he offered her a lift when she was standing at a bus stop. Wilson's press secretary Joe Haines claims that the pair first met at a dinner with the Soviet premier, Nikita Khrushchev, at which Khrushchev and the Labour MP George Brown had a drunken argument, which Williams took down in shorthand. Wilson reportedly drove her home after dinner. In 1970 she was appointed a Commander of the Order of the British Empire (CBE).
Questions were raised in the press at the time about her commercial dealings; however, both Wilson and Williams successfully sued many London newspapers for libel. Later Harold Wilson publicly called for a Royal Commission of Inquiry into the press because of the defamation in the media, and that there had been a concerted smear campaign to de-stabilise his administration by MI5. Later these claims were corroborated by Peter Wright, former assistant director of MI5, in his book Spycatcher. Spycatcher was banned in the UK by Margaret Thatcher's administration.
Until 1966, the award of peerages was the prerogative of the Chief Whip, and not the Prime Minister. Wilson took that power to award peerages for himself, and later told his policy adviser Bernard Donoughue that he did it because "that gal Marcia insisted on it". Donoughue's diary recorded Wilson telling one of his staff that he had just quarrelled with Falkender, who was demanding "peerages for friends". Donoughue's diary actually credits the "that gal Marcia insisted on it" comment to Freddie Warren who ran the Chief Whip's office in No. 12 Downing Street from the mid-fifties and was still in situ when Wilson resigned as Prime Minister in March 1976.
When Wilson resigned, Haines accused Falkender of writing the first draft of his Resignation Honours List on lavender paper, which Haines styled as the "Lavender List". Haines was never asked to produce any evidence for this claim, and to date none has been provided. Certainly Wilson's honours list included many businessmen and celebrities, along with Labour supporters. In a BBC Panorama programme aired on 14 February 1977 called to clarify his book, Haines explicitly and unequivocally denied any financial impropriety in the compilation of the list.
Wilson's choice of appointments caused lasting damage to his reputation; former Home Secretary Roy Jenkins noted that Wilson's retirement "was disfigured by his, at best, eccentric resignation honours list, which gave peerages or knighthoods to some adventurous business gentlemen, several of whom were close neither to him nor to the Labour Party." In the 1990s two large academic biographies of Wilson were published by Philip Ziegler and Ben Pimlott. Both authors stated that there was no financial impropriety in the compilation of the list. Pimlott observed in his biography of Wilson that political secretaries often write down lists at the instructions of their employers, and that in this case the fact that the list was pink does not itself prove anything. Both Falkender and Wilson maintained that the list was Wilson's.
She herself was elevated to the Peerage as Baroness Falkender, of West Haddon in the County of Northamptonshire on 11 July 1974. Falkender had been her mother's maiden name.
Although Falkender attends sittings in the House of Lords and votes, she has never made a maiden speech. She is currently the longest serving Labour member of the House of Lords.
Following her peerage, Private Eye often referred to her as "Forkbender", an oblique reference to the contemporary activities of Israeli illusionist Uri Geller.
She has written two books about her time in Downing Street: Inside Number 10 on the period 1964–1970 and Downing Street in Perspective on Wilson's third term as Prime Minister 1974–1976. After retiring from working in Downing Street, she worked as a columnist for the Mail on Sunday from 1983 to 1988. She continued to work for Wilson, handling his private business from the time of his resignation in 1976 until his death in 1995.
She was also one of the founder members of The Silver Trust, a charity which sponsored British silversmiths to provide a silver service for 10 Downing Street. Prior to The Silver Trust, Downing Street had no silverware of its own; it was provided on loan from other government offices.
She was one of the sources inside Whitehall used by the writers of the comedy series Yes Minister, the other one being Lord Donoughue.
In 2001 Joe Haines re-wrote his original book, The Politics of Power, making allegations about Falkender. The BBC delayed the screening of a docudrama based on the book. After the programme was aired in March 2007, Falkender sued the BBC for libel, and was awarded £75,000. The BBC promised never to rebroadcast the programme.
Marcia Field married George Edmund Charles Williams in 1955, but they divorced in 1961; she continued to be known as Marcia Williams in her professional life. Falkender had two sons in the late 1960s by the former political editor of the Daily Mail, Walter Terry. When Wilson lost office in 1970, Falkender seized his papers, and her brother, Tony Field, helped Wilson break into her garage to recover them. On her brother's wedding day, in 1973, his passport, airline tickets and money disappeared. Field called the police, who were told by Falkender that she had put them away for "safe keeping".
In 1967, Wilson sued the pop group The Move for libel after the band's manager Tony Secunda published a promotional postcard for the single "Flowers in the Rain", featuring a caricature depicting Wilson in bed with Falkender. Wilson won the case, and all royalties from the song were assigned in perpetuity to a charity of Wilson's choosing.1932–1955: Miss Marcia Field
1955–1970: Mrs Marcia Williams
1970–1974: Mrs Marcia Williams
1974–: The Rt Hon. The Baroness Falkender