Carlos Sainz will join Renault earlier than planned after the team mutually agreed to part company with Jolyon Palmer following this weekend's Japanese Grand Prix.
Sainz had already agreed a move to Renault from Toro Rosso for 2018, at Palmer's expense.
Yet the Briton will now give up his position after Sunday's race at Suzuka, with Toro Rosso agreeing to let Sainz fill the void for the year's final four races.
Daniil Kvyat will regain a seat at Toro Rosso as a result, alongside Pierre Gasly, who replaced the Russian in Malaysia.
The various moves were confirmed in media releases by Renault and Toro Rosso on Saturday, after Palmer had revealed his imminent exit from the French team in an Instagram post.
"I would like to thank Toro Rosso and Red Bull for allowing me the possibility of finishing this season with Renault Sport Racing," said Sainz.
"Toro Rosso is made up of a fantastic group of people and I wish them only the best for the future. On my side, I will definitely do my very best in tomorrow's race... this would be the best possible send-off.
"Additionally, competing in these last four races with Renault gives me a good opportunity to get to know the team and the car earlier than expected. I am looking forward to start working with them."
Renault managing director Cyril Abiteboul thanked Palmer for his commitment and professionalism, adding: "Since Renault's return to Formula 1, Jolyon has been highly dedicated in an evolving environment. He has shown great personal qualities and we wish him all the best in his future career."
Palmer has picked up just eight points so far this term, 40 fewer than Sainz's tally for Toro Rosso.