Caldwell attended Auckland Grammar School and acquired British/New Zealand dual nationality.
Drivers he worked with included Emerson Fittipaldi, James Hunt and Jochen Mass.
He was involved in the design, production and preparation of the cars for racing and was the inventor of an air-starter to make the cars lighter and also introduced a sixth gear, skirting to increase down force and team uniforms to replace the assortment of overalls and other clothes that were previously worn.
He was a technical advisor on the 2013 film Rush about the rivalry between the drivers James Hunt and Niki Lauda during the 1976 Formula One motor-racing season.
In the film he was portrayed by Stephen Mangan and he also had a cameo role on screen as a race official.