The appointment adds £20 million in billings to Saatchis' existing £40 million UK account.
The London agency worked with the Paris office to win the business from Paris-based Lowe Alice, competing against its fellow Publicis network Leo Burnett.
Saatchis will work with the Brussels-based Toyota Motor Marketing Europe on creative and strategic advertising, but will also advise existing marketing agencies in unspecified local areas that retain their positions on the Toyota roster.
As well as taking the European Avensis brief - the pitch for which was scrapped following Saatchis' overall win - it is thought the network will also take on other branding projects in Europe, such as the relaunch of Toyota's Yaris supermini brand.
The consolidation comes as Toyota seeks to build on booming sales in Europe this year, which grew 21 per cent in the six months to September 2002 in a falling market.
Toyota wants further growth in the region and plans to overtake Mercedes and Citroen to become Europe's number eight marque. It has told dealerships it wants to sell 1.2 million units a year - half as much again as its current targets - by 2010.
Saatchis refused to comment on the appointment.