The result will be an all-new MX-5 and a new Alfa Romeo roadster. Both vehicles will be built at Mazda's factory in Hiroshima, Japan, but with different styling and engines.
Production of the new Alfa Romeo model is due to start in 2015, while the new MX-5 is likely to arrive in 2014.
Fiat boss Sergio Marchionne said: 'By partnering with Mazda we will be co-operating with the recognised leader in compact rear-drive-vehicle architectures in order to deliver an exciting and stylish roadster in the Alfa Romeo tradition'.
The new MX-5 will use Mazda's efficient 'Skyactiv' technology a combination of lightweight construction and new engines that made its debut on the new CX-5 SUV.
The official announcement doesn't say whether Alfa Romeo and Fiat will be able to use the technology for other models, but it does confirm that both manufacturers 'have agreed to discuss further opportunities for co-operation in Europe'.
The final agreement is expected to be signed later this year.