As expected by Motorsport.com, the winner of the 2008 Canadian Grand Prix will join George Russell at Williams next year and complete the absence of F1 in the grid for more than eight years.
Kubica did not participate in Formula 1 races since the end of the 2010 season, sustaining serious injuries to his right hand as a result of a rally in early 2011.
Having secured a place as a starting driver for 2019, this means that Kubica will complete an amazing recovery from the injuries he suffered as a result of this accident, which prevented him from competing for several years.
Kubica, who says he now treats "70%" with his left hand, has not participated in single seats since his last Grand Prix in Formula 1.
His first sporting activity after the accident was at rallies, before returning to the race in the GT race for 12 hours of Mugello in 2016.
Kubica completed a successful test last year with the 2012 Renault F1, before driving 2017 Renault and Williams in Hungary and Abu Dhabi respectively.
The agreement with Williams means that the 33-year-old gets a seat, which he originally offered this season, before agreeing to the role of a backup driver.
It is believed that Kubica received a firm offer from Ferrari to take on the role of development with the Italian team by 2019.
Robert Kubica, Williams FW41
Photo: Andrew Hone / LAT Images