•The team said last month that the 21-year-old would be given the drive alongside Alex Albon if he secured the required points for an F1 licence.
•Finishing fourth in the Formula 2 championship at the final race of the season in Abu Dhabi has taken Sargeant well over the 40 points required.
American Logan Sargeant has secured the final seat on next year's Formula 1 grid with Williams.
The team said last month that the 21-year-old would be given the drive alongside Alex Albon if he secured the required points for an F1 licence.
Finishing fourth in the Formula 2 championship at the final race of the season in Abu Dhabi has taken Sargeant well over the 40 points required.
Williams are expected to confirm the move in the coming days.
Team principal and chief executive officer Jost Capito said at the US Grand Prix: "We feel he's ready to race in F1 and on the condition he has enough super-licence points he will be our second driver next year."
Sargeant's promotion confirms that Mick Schumacher, who has raced for Haas for the last two years, has lost his place in F1.
The US-based team announced on Thursday that they had signed German veteran Nico Hulkenberg as Kevin Magnussen's team-mate in 2023.
Hulkenberg had been without an F1 seat since being dropped by Renault at the end of the 2019 season, although he has made a handful of substitute appearances for the Racing Point/Aston Martin team after Sergio Perez, Lance Stroll and Sebastian Vettel contracted Covid-19.
Schumacher, son of seven-time world champion Michael, wants to return to F1 as soon as possible.
"There are different opportunities and I am strongly planning to be back in 2024," he said.
He is tipped to become Mercedes' reserve driver. No formal talks have yet taken place between the two parties but Mercedes team principal Toto Wolff said: "Mick is someone that has always been close to our heart because of Michael or the whole Schumacher family.
"Ralf [Michael's brother] was in a DTM [car] for a long time for us, his son races Mercedes in GTs, and Mick is an intelligent, well-mannered young man.
"He's been very successful in junior formulas. We believe that we can look after him if the situation were to happen and with someone that just fits the team.
"But we haven't really put pen to paper, we haven't really come anywhere close to any terms. I think he just fits and now we need to make it happen, if he wants to, Sabine [Kehm, Schumacher's manager] wants to and then we see we see where that goes to."
Schumacher said: "Mercedes is an awesome brand. What they've achieved in F1 is incredible so for sure I'm looking at all options and Mercedes is part of that.
"My dad did the switch from Ferrari to Mercedes at the time. I don't see any reason why not now but I have time now so I will consider all the options I have to then make the right decision for me.
"But it's definitely very humbling to hear what Mercedes - and especially Toto - says about me."