Dewrance was educated at Charterhouse School before entering King's College, London, where he is said to have "paid special attention to chemistry".

The following year he took over the research laboratory and staff of Professor Frederick Barff, where he experimented on protecting iron from rust.

[2] Dewrance went on to enjoy exceptional success as an inventor and mechanical engineer, taking out a total of 114 patents relating to steam fittings and boiler mountings.

[3] By sheer coincidence, the former Dewrance & Co. headquarters on Great Dover Street now forms part of a King's College hall of residence.

[8] The Sir John Dewrance prize is awarded to the two best mechanical engineering students each year at City, University of London.