The Lotus 33's development was based on the earlier Lotus 25 model, taking the monocoque chassis design to new development heights. The 33 was again powered by the 1500 cc Climax engine. The 33 was almost identical to the 25, but had suspension designed around newer, wider tyres. The car was more rigid and was simpler to build than its predecessor.

Six Lotus 33s were constructed, with chassis numbers following on from the 25 and beginning with R8. One chassis, R12, was modified to take the stillborn Climax FWMW flat-16 engine; this car was designated the Lotus 39. Chassis number R13 was not used by Team Lotus but was later unofficially adopted by Reg Parnell Racing for their crashed chassis R4, rebuilt around a 33 chassis.[2] The last of the series, R14, was built with a 2-litre version of the Climax V8 for the 1966 World Championship season, pending the arrival of the Lotus 43.