Williams will continue to race with Mercedes power units until the end of the 2025 season.
Williams became a Mercedes customer team at the start of the 2014 season, using its power units and engines en route to third place in the constructors’ championship in each of the first two years of the partnership.
“We have enjoyed a wonderful partnership with Mercedes-Benz over the past six years of what was originally a seven-year agreement, and so we are delighted to be continuing working with them for a further five years from 2021,” said deputy team boss Claire Williams.
“Mercedes-Benz has been one of the sport’s most successful engine suppliers and we believe that they will continue to have an extremely competitive engine package going forwards.
“Over our time with them they have become a real friend of the team, and we look forward to working with Mercedes-AMG HPP in future.”