He began his studies at Hornsey College of Art in 1938, with a five-year break from 1942 to December 1946 in the Royal Engineers, most of which was spent in North Africa and Italy.
In 1950 he began working as a freelance illustrator, for London Zoo, The Radio Times, Crawfords Advertising Agency and Collins.
[6] Ovenden was commissioned by the Open University to prepare a poster accompanying David Attenborough's BBC series Life in Cold Blood.
After a period of 15 years' work, Galápagos, a Guide to the Animals and Plants[7] finally went to print after the addition of illustrations of two other recently discovered rodents and the elusive pink iguana.
[8] An illustration of Ifield Water Mill in West Sussex was painted by Ovenden in 2015 and shows a scene from 1848 when the railway between Crawley and Horsham crossed the millpond on a wooden trellis viaduct.