Nicholas Latifi has been confirmed as George Russell's team-mate at Williams for next season.
The 24-year-old Canadian, who has taken part in a number of practice sessions for the British team this term, replaces the departing Robert Kubica.
Williams' move to confirm Latifi ahead of this weekend's season-concluding Abu Dhabi Grand Prix completes the driver market for 2020.
It means Renault's Nico Hulkenberg, who made his debut in 2010 and has racked up 176 appearances, will be without a seat next year.
Latifi's step up from his role as reserve driver had been widely expected following the announcement in September that Kubica's short-lived comeback to the sport would be coming to an end.
Sunday's race in Abu Dhabi will be the Pole's last in Formula One.
Kubica, 35 next month, has struggled for speed since his remarkable return to the grid eight years after a life-threatening rally crash. But the Pole has scored the team's only point, finishing 10th at July's German Grand Prix, in what has been a desperate year for Williams.
Latifi, who is second in Formula Two, the feeder series to F1, ahead of the final round this weekend, said: "I am thrilled to be stepping up as race driver for 2020.
"I have thoroughly enjoyed working with the team this year, supporting them with the development of the car, and assisting wherever I can trackside and at the factory.
"I look forward to the journey ahead with the team, and I am excited to make my Formula One debut at the Australian Grand Prix in 2020."
Deputy team principal Claire Williams added: "All of us at Williams have been immensely impressed at what Nicholas has achieved this year in Formula Two, along with his commitment to the team, and the work that he has put in behind the scenes.
"Nicholas has become an established and well-respected member of Williams, and we look forward to him stepping up into this new role, as we look to fight our way back to the midfield."