A list of the titles Lady Soames held in chronological order from birth:

15 September 1922 – 1945: Miss Mary Spencer-Churchill
1945 – 11 February 1947: Miss Mary Spencer-Churchill, MBE
11 February 1947 – May 1965: Mrs. Christopher Soames, MBE
May 1965 – 1972: The Hon. Mrs. Soames, MBE
1972 – 19 April 1978: The Hon. Lady Soames, MBE
19 April 1978 – 14 June 1980: The Rt Hon. The Lady Soames, MBE
14 June 1980 – 23 April 2005: The Rt Hon. The Lady Soames, DBE
23 April 2005 – 31 May 2014: The Rt Hon. The Lady Soames, LG, DBE

Mary Spencer-Churchill was raised at Chartwell and educated at the Manor House at Limpsfield. She worked for the Red Cross and the Women's Voluntary Service from 1939 to 1941, and joined the Auxiliary Territorial Service with whom she served in London, Belgium and Germany in mixed anti-aircraft batteries, rising to the rank of Junior Commander (equivalent to Captain). She also accompanied her father as aide-de-camp on several of his overseas journeys, including his post-VE trip to Potsdam, where he met with Harry S. Truman and Joseph Stalin.

She served many public organisations, such as the International Churchill Society, as a Patron; Church Army and Churchill Houses; and chaired the Royal National Theatre Board of Trustees between 1989 and 1995. She was Patron of the National Benevolent Fund for the Aged.

A successful author, Lady Soames wrote an acclaimed biography of her mother, Clementine Churchill, in 1979. She offered insights into the Churchill family to various biographers, prominently including Sir Martin Gilbert, who became the authorised biographer of Sir Winston Churchill after the death of Churchill's son, Randolph, in 1968. Additionally, she published a book of letters between Sir Winston and Lady Churchill, editing the letters as well as providing bridging material that placed the letters in personal, family, and historical context.

One of her more notable public appearances came on 29 April 2002 when she dined with the Queen at Buckingham Palace as part of the Golden Jubilee celebrations, alongside prime minister Tony Blair, and the four surviving former prime ministers at the time, as well as several relatives of other deceased prime ministers.

Lady Soames was honoured with becoming a Dame Commander of the Order of the British Empire for her public service, particularly in Rhodesia. She was appointed a Lady Companion of the Order of the Garter on 23 April 2005, and was invested on 13 June at Windsor Castle.

On 31 May 2014, Lady Soames died at her home in London at the age of 91 following a short illness.

She was a distant cousin of Diana, Princess of Wales (1961–1997), mother of the heir to the throne His Royal Highness Prince William of the United Kingdom, Duke of Cambridge, through the Spencer family.

portrait of Mary Churchill, painted by the Belgian painter Louis Rigaux in Overijse (Belgium) in 1945

Colorized photo of Mary Soames in 1965.

Mary Soames with her father.