Judy was born in 1939 in Hampstead,West London, to Norman Frederick Grinahm and Flora Edith Grinham. Six months after she was born her father was sent to France as part of the British Expeditionary Forces, having survived Dunkirk, he was then posted to the Middle East and did not return until Judy was nearly 7 years old. On his return, to build a relationship with his daughter he took her swimming in the open air pool in Gladstone Park, Neasden.
Over the next few years Judy learnt to swim so well that he put her up for trials at the newly formed Hampstead Ladies swimming club. She trialled three times before they felt she was good enough to join the club, and in January 1950 she was finally given a place. Her progress was slow at first, but she was determined and motivated to do well. As she gradually began to improve she started to train regularly, but training in those days was not the same as the Olympic athletes of today. She would train in public swimming pools, with no dedicated lanes, dodging members of the public. No training facilities, no sponsorship deals, the sport was strictly amateur, and the cost was funded by her family.
Over the next five years, slowly but surely, Judy began to start winning and eventually progressed to national competitions. Six years later, in 1956, at the age of 17, she was picked for the Olympic squad and went to the Melbourne Olympics, where she outswam the favourite and by a hairs breadth won the Olympic Gold Medal in a new world record time (and the first British Swimming Gold Medallist for 32 years). She also went on to be the first athlete in any sport to hold the Olympic, Commonwealth and European gold medals at the same time.
Judy retired at her peak and went on to report on the 1960 Rome Olympics for the Daily Express. Many years later she was appointed a Member of the Order of the British Empire (MBE) in the Queens Birthday Honours list, a full 50 years after winning gold inMelbourne.