Two-time world champion Alonso announced on Tuesday that he had decided to leave McLaren and “move on” from F1 at the end of the season.
“I’m delighted to finally be able to confirm that I’ll be a McLaren driver from the 2019 season,” Sainz said on the team’s official website.
“It’s something I’ve been looking at for a while and I’m very excited about this next chapter in my career.
“I’ve been a McLaren fan for as long as I can remember. It’s a great name in the sport with an incredible heritage, and the list of drivers that have raced for McLaren over the years are among the heroes of Formula 1.”
