Marion Katherine Blight was born in Watford in 1921. Her mother worked in domestic service while her father was a shop assistant. McQuillan attended Wycombe High School before getting a scholarship to Henrietta Barnett’s School. McQuillan went to University in 1939 where she graduated from Girton College, Cambridge with a degree in metallurgy and natural sciences. She got her first job in 1942 in the Royal Aircraft Establishment Farnborough (RAE) in 1942. McQuillan researched jet engine metals and was  a member of the first team to research titanium.
In 1946 she  travelled through Germany and Austria as member of one of the many teams sent by the British Intelligence Objectives Sub-Committee, collecting technical information from universities, research establishments and factories.
She also worked at the Atomic Energy Research Establishment at Harwell, working on some of the early metallurgical problems of nuclear energy. From 1948-1951 she was at the Australian Royal Aircraft Establishment in Melbourne.
McQuillan returned to the UK where she began to work for ICI Metals (also known as IMI), in the Titanium Alloy Research Department where, within two years later she was head of the section. With her husband McQuillan published the seminal book “Titanium” in 1956. During the 1960s McQuillan registered 8 titanium alloy patents. In 1967 McQuillan was appointed technical director of the New Metals Division and by 1978 she became the first woman managing director of Imperial Metal Industries subsidiary, Enots.