In 1957 Opel Product Director Karl Stief was mandated by General Motors headquarters in Detroit to develop "the perfect Anti-Volkswagen" ("einen perfekten Anti-VW"). The development team was headed up by Stief, supported by Hans Mersheimer (car-body) and Werner K. Strobel (engine and running gear), under conditions of such secrecy that even now very little is known of the development history of the 1962 Kadett. It has been alleged that GM was trying to conceal a new technique of platform and design sharing between Opel and its British sister company Vauxhall, which released the strikingly similar Viva HA in 1963, a year after Opel introduced the Kadett. Over the subsequent two decades Opel and Vauxhall's ranges would rapidly converge as Vauxhall's design independence from Opel was eroded to the point where by 1985, Vauxhall's car range entirely consisted of rebadged Opel models.
The GSi's engine mapping had been carried out by Opel tuning specialists Irmscher. A model with the 82 PS (60 kW) 1.4 L multi point fuel injected engine, which was otherwise mechanically identical to the GSi, also became available as the Nova SRi in the United Kingdom. In January 1988, a turbocharged version of the Isuzu diesel engine was introduced, with power increased to 67 PS (49 kW).