Former champions Williams will switch to Toyota engines next season in a three-year deal they believe can take them back to the top in Formula One.
"This agreement is the cornerstone of Williams's challenge for the world championship," team boss Frank Williams said yesterday.
"Toyota is an impressive and remarkable industrial giant, with the most phenomenal reputation for achieving the goals it sets itself. We are proud to have secured their support in our efforts to return to our competitive best."
Williams, who are powered by privately-owned Cosworth this season after separating from BMW, said they would use the same specification engines as Toyota's own team.
The long-awaited announcement will mean the end of Toyota's current agreement with uncompetitive tail-enders Midland.
Williams, owned 70 per cent by the team boss and 30 per cent by co-founder Patrick Head, have won 113 grands prix since 1979 and nine constructors' championships.
Their last titles were in 1997, when Canadian Jacques Villeneuve also won the drivers' crown.