Williams have confirmed that they will be using Mercedes engines with effect from the 2014 Formula 1 season.
Williams are powered by Renault engines since the 2012 season.
Their new partnership will see Mercedes supplying them with 1.6 litre V6 turbocharged engines, part of the new regulations effective from 2014.
"Under the terms of the agreement, Williams will be supplied with a Mercedes Power Unit (Internal Combustion Engine plus Energy Recovery System) by Mercedes High Performance Powertrains (HPP) based in Brixworth, UK. Williams will continue to manufacture its own transmission," said the Grove outfit in a statement.
The 2014 regulations will set the sport's engineers the challenge of completing a 300 km race distance on a fuel load of just 100 kg.
Speaking about the new engine partnership, Williams team principal Sir Frank Williams said: "I'm delighted to announce our new association with Mercedes-Benz.
"Mercedes-Benz has been one of the sport's most successful engine suppliers and we believe that they will have an extremely competitive engine package. I would also like to take this opportunity to thank Renault for their continued hard work since we renewed our engine partnership at the beginning of the 2012 season. We have enjoyed a strong relationship that has resulted in much success over the years, including powering us to winning ways once again last year at the Spanish Grand Prix."
Claire Williams, deputy team principal, said: "The announcement of this partnership is exciting news for Williams. Securing the right engine supply partnership is a key milestone in the implementation of our strategy for long term success. We are also pleased to conclude this agreement early in the season and we very much look forward to working with Mercedes in developing our 2014 race car."
Williams are yet to score a point this season.