Marjorie Jean Oswald Kennedy hailed from the Kennedy family of Kilmarnock which included Thomas Kennedy c1796-1874, founder of Glenfield & Kennedy (producers of valves) and inventor of the world's first water meter.

During the Second World War, Kennedy served with the Women's Royal Naval Service (WRNS), 1942-1945. She was stationed at HMS Pembroke III, the WRNS training depot at Mill Hill in 1942, then at HMS Beaver, Hull, from 1942 to 1943, at HMS Drake, Devonport, in 1943, and then at HMS Pembroke III again and HMS Pembroke V, Bletchley Park, between 1943 and 1945. At Bletchley Park she was working with the team of allied codebreakers who were able to decrypt a vast number of messages that had been enciphered using the German's Enigma machine. The intelligence gleaned from this source, codenamed 'Ultra' by the British, had been a substantial aid to the Allied war effort.

In the 1960s and 1970s she was living in London, but by the early 1980s residing in Edinburgh and working at Edinburgh University Library. Kennedy served as an Elder at St. Cuthbert's Parish Church, Edinburgh, and lived in the Marchmont district of the city. She had been the inspiration behind the founding of the Rock Trust - a charity for homeless people.

Marjorie Jean Oswald Kennedy died in November 2002 aged 87. In August the following year there was local press coverage of the large fortune of £1.5-million left in her will and which had been inherited from her family.