Mansell, who won the world drivers' championship in a Williams in 1992, will drive the final four races on the IndyCar schedule, then join Williams for the last three grands prix of the 1994 season: the European Grand Prix at Jerez, Spain, on 16 October, the Japanese race at Suzuka on 6 November and the Australian in Adelaide on 13 November. He will become team-mate to his fellow Briton, Damon Hill, replacing David Coulthard.
Mansell has already driven for Williams at the French Grand Prix in early July during a break in the IndyCar season, but after winning the IndyCar title in his first season of racing in 1993, he has not won a race this term and is sixth in the standings.
Frank Williams, the team principal at Williams, said: 'I think Nigel enjoyed his race in France and the fact he is prepared to come back for the final three seems to underline this. Nigel never takes an easy option and coming to Formula One after two seasons in another series confirms this.'
Although Mansell has been released from his 1995 contract with Newmaan-Haas, Williams would make no comment about the possibility of him rejoining the team for the 1995 season.
One compelling reason for Mansell to consider returning to Formula One for a whole season would be the possibility of his becoming the oldest world drivers' champion in the era of hi-tech racing.
Mansell is now 41 and has the example of Juan Fangio, the great Argentinian, who is the oldest drivers' champion on record: he was 45 when he won the last of his five titles in 1957.
The American team with which Mansell has enjoyed unprecedented success - he was the first driver to win the IndyCar title in his rookie season - was run by the the motor racing entrepeneur and race promotor, Carl Haas, and the actor, Paul Newman.
Haas said yesterday: 'Paul and I enjoyed our success with Nigel. We wish him the best of luck in the future and I know our friendship will continue. We became friends and made history together.'