The deal is worth a colossal £100 million in showroom prices over four years.
Vauxhall Motors will supply the largest single batch of vehicles, primarily Astras and Vectras for Rentokil's fleet of 3,600 cars, and also car-derived vans and light commercial vehicles up to 3.5 tonnes for its 1,900 commercial vehicle fleet.
The deal replaces a primarily Ford single badge arrangement in the UK, GM said.
In the rest of Europe, the company is taking delivery of 1,200 vehicles in the Netherlands, 700 in Germany, 650 in Belgium, 1,350 vehicles for part of its French fleet and a further 1,300 vehicles in another 11 countries from Finland to Greece.
Earlier this year, Rentokil invited six manufacturers to tender for the business after carrying out an internal appraisal of its Europe-wide vehicle requirements.
Rentokil's procurement director Mike Tunnell said: 'General Motors Europe offered us the optimal financial solution in terms of price and wholelife costs, and appropriate logistical and service solutions in terms of vehicle suitability, availability and fleet service levels back-up.'
In the UK, the cars will mainly be operated on a three year/75,000 mile replacement cycle and the commercial vehicles on four years/100,000 miles.
Rentokil's procurement manager Ian Lathey said the company had already noticed a 'swing towards diesel' in the UK in response to the CO2-based benefit-in-kind company car tax system, and that it expected the trend towards diesel to grow.
Vauxhall Motors fleet director Maurice Howkins, who carried out the negotiations in the UK in conjunction with General Motors Europe fleet manager Georges Megyeri, said: 'The size of the contract, the fact that it was won against stiff competition from other major manufacturers and the level of services involved all combined to make this a very satisfying contract from a General Motors point of view.'