Spa-Francorchamps - Valtteri Bottas will remain as Lewis Hamilton's Mercedes team-mate next year while Esteban Ocon will replace Nico Hulkenberg at Renault, the teams announced Thursday.
Frenchman Ocon's return to a race seat after a season spent as test and reserve driver with Mercedes was announced soon after the champions Mercedes had decided to give Bottas a fourth year alongside five-time champion Hamilton.
On a busy first day back after the European summer shutdown, the Formula One paddock was alive with transfer talk and other speculation including a likely return to action by Marcus Ericsson at Alfa Romeo ahead of the Belgian Grand Prix on Sunday.
Mercedes have exercised an option to retain Bottas, who was 30 on Wednesday.
Since joining Mercedes in 2017, the Finn has won five Grands Prix and is second by 62 points behind Hamilton in this year's title race.
"My overall target is to become Formula One world champion. I believe that on paper, and from my experience with the team, Mercedes is the best option for me to achieve that goal in 2020," said Bottas.
Team chief Toto Wolff said Bottas had shown his best form this year and remained "hungry for more and determined to keep on improving and raising his level - the mind-set we want from all our team members."
After a winless season, Bottas bounced back this year with two wins and seven other podium finishes to emerge as Hamilton's main rival as the Briton bids for a sixth title.
"We have a great working relationship, Valtteri and I, and he's constantly improving," said Hamilton.
"I think it was a smart decision from the team, to be honest... We get on well both outside and on the track.
"He wakes up and wants to beat me. I wake up and I naturally want to beat him, but we shake each other's hands as men."
At Renault, Ocon signed on a two-year contract as team-mate for Daniel Ricciardo in a bid to boost the French team's competitiveness, a move that has left the widely-liked Hulkenberg in search of a vacant seat for 2020.
"First and foremost, I am very proud to become a Renault driver," said Ocon, formerly a test driver with the team. "I have grown up at Enstone, starting with Lotus in 2010 and then with Renault.
"I am very attached to this team and everyone who works there -- they are the ones who opened the doors of top level motorsport for me.
Hulkenberg was praised for his work with the team. Renault team boss Cyril Abiteboul said he had made a "phenomenal contribution."
"When Nico decided to join us, the team was ninth. He brought us to fourth place last year and was classified seventh in the drivers' championship.
"The imminent end of his contract made this decision a difficult one as Nico has been a pillar of this progress.
"The first part of this season has been more challenging, but I know we can count on him and deliver together throughout the second half of the year."
Ericsson's return could be confirmed if Kimi Raikkonen fails a fitness test after pulling a leg muscle.
"Obviously, we need to have some back-up plans. It would be stupid not to have our third driver in case I couldn't be driving, then it is the worst-case scenario.
"It is a difficult situation for him [Ericsson] also because he had a race, but that is how it is. I would say it is getting better, so we will see how it is."
Swede Ericsson, who was demoted to test and reserve driver last year, was scheduled to take part in an IndyCar race in Portland this weekend.