Paul di Resta will return to Formula 1 this season as Williams' reserve driver, BBC Sport has learned.
The Scot, who drove for Force India from 2011-13, will attend most of the races in his new role as back-up for Valtteri Bottas and Felipe Massa.
Di Resta, 29, will continue racing for Williams' engine partner Mercedes in the German Touring Car Championship.
Williams were unavailable for comment but sources said the deal would be announced in the coming days.
The 2016 F1 season starts in Melbourne, Australia next weekend.
Di Resta's appointment comes as something of a surprise - it was widely assumed his F1 career was over after he was dropped by Force India three years ago.
But his new role means he could race again if either of the Williams race drivers are indisposed.
The team started last season without a reserve driver but appointed Di Resta's former team-mate Adrian Sutil to the role when Bottas injured his back at the season-opening Australian Grand Prix and was temporarily in doubt for the next event in Malaysia.
The team also have British GP2 racer Alex Lynn on their books as development driver, a role the 22-year-old also performed last year.
Canadian Lance Stroll, 17, who races in European Formula Three, is also under contract to Williams in a development role.