The deal follows Williams' split from BMW.
The parties say the partnership is not be based on a traditional engine supply agreement, and will see both WilliamsF1 and Cosworth invest in the programme.
The scope of the collaboration includes not just the engine, but extends to a programme of design and development for the entire drivetrain package (spanning engine, transmission, associated electronics, software and installation architecture).
The Williams deal is notable for not being one with a major car manufacturer, some of which are behind plans for a potential breakaway series.
Patrick Head, WilliamsF1’s director of engineering, said: “Williams has made this partnership decision purely on technical merit. Among the range of options we considered, Cosworth are very well advanced with existing development and are committed to taking the potential of this collaboration further."
