Kimi Antonelli to replace Lewis Hamilton at Mercedes in 2025
Team boss Toto Wolff told reporters at Monza he had decided on Antonelli within minutes of Hamilton informing him last January that he would be moving to Ferrari in 2025.
"Instinctively that is the line-up, with these two, that I always wanted," said the Austrian, who expected "great things" from the youngster but also plenty of mistakes along the way.
Antonelli, who joins race winner George Russell in the lineup, has been competing in Formula Two this year but has been supported by Mercedes since 2019, with a programme of private testing in older cars this year.
He will be the first rookie to drive for Mercedes in 70 years, already a daunting enough prospect without also stepping into the shoes of the most successful driver in the history of the sport.
The announcement came a day after Antonelli, who will also be the most high-profile rookie since Hamilton debuted with McLaren in 2007, crashed Russell's car in his free practice debut at Monza.
"It's not possible to replace Lewis Hamilton, he's such a great figure in the sport of today and he has achieved so much in his career," said the Italian, who will race next season with the number 12.
"I'm just the next driver for Mercedes in '25, so I'm really excited for that."
Wolff had also sounded out Red Bull's triple world champion Max Verstappen about a possible move but the Dutch driver is under contract to the end of 2028 and the overtures came to nothing.
"These two are the future," said Wolff.
"All of our focus in the team is on George and Kimi. There's no discussion, there are no second thoughts about what we're doing in 2026 because now it's about 2024 and 2025."
Antonelli will be the first Italian driver to race in Formula One since Antonio Giovinazzi in 2021 and the first with a top team since Giancarlo Fisichella stood in at Ferrari in 2009.
Fisichella is also the last Italian to win a race, with Renault in 2006.
"Reaching F1 is a dream I've had since I was a small boy. I am still learning a lot, but I feel ready for the opportunity," Antonelli said in the statement announcing his arrival.
"I'm also really excited to become George's team-mate. He came through the team's junior programme just like myself and is someone I have a huge amount of respect for ... I am looking forward to learning from him and working together to deliver on track."
Russell, who will be starting his fourth season at Mercedes, also looked forward to the new pairing.
"I know how much of a support Lewis was for me throughout my time as a junior driver and since I've been his team-mate. I've learned so much from him and I hope to play a similar role for Kimi," he said.
Mercedes have won three races so far this season, Hamilton taking two of them.