Although born in Berkhamstead, John Eddy spent his early years in Argentina where his father was a railway manager. Eddy returned to England at the age of eight to be educated at the Stanmore Park Preparatory School, before going to Stowe School, and then to the London Polytechnic. In 1935, at the age of 20, he became a student at the Institute of Mechanical Engineers in London. Eddy was one of the six crew members aboard Saskia in the 8-metre event at the 1936 Olympics, despite being just 21-years-old at the time. After showing early promise, finishing fourth in races one and two, they never managed such a highly placed finish in the remaining races and finished sixth overall.