Brazilian Felipe Massa will replace Venezuelan driver Pastor Maldonado at Williams next season after signing a multi-year contract, the Formula One team announced on Monday.
Finland's Valtteri Bottas will remain as the former champions' other driver.
"When I was a kid I always dreamed about racing for Ferrari, Williams or McLaren," Massa said in a statement before addressing assembled Williams employees at the factory in central England.
"I'm glad to be signing with another icon of the sport following my time at Ferrari."
The 32-year-old has raced for Ferrari since 2006 with 11 Grand Prix wins during that period. He missed out on the world championship by a single point in 2008 to Britain's Lewis Hamilton, who won the title in heartbreaking fashion for Massa after overtaking Timo Glock on the final corner of the Brazilian Grand Prix.
He follows in the footsteps of the late triple champion Ayrton Senna, Nelson Piquet, Rubens Barrichello and Bruno Senna as Brazilians to have driven for Williams.
"He is an exceptional talent and a real fighter on the racetrack," said team principal Frank Williams. "He also brings a wealth of experience as we begin a new chapter in our story."
Ferrari have already announced that 2007 world champion Kimi Raikkonen, who is out of contract with Lotus at the end of the season, will replace the Brazilian at the Italian team.
Maldonado brought substantial backing from Venezuelan oil company PDVSA to Williams when he arrived in 2011 but has become frustrated with the former champions, who have scored just one point this season.
Williams thanked him for his efforts, in particular his victory in last year's Spanish Grand Prix.
"This announcement is a key step towards our goal of returning Williams to the front of the grid, and part of our ongoing plans to ensure we are stronger in 2014 and beyond," said deputy principal Claire Williams.
"The stability of having both our drivers on multi-year contracts, Mercedes-Benz as our engine partner and a strong commercial base all contribute to the future success of the Williams F1 team."
Fresh from farewell
Massa said 2014, with a new V6 engine being introduced and major rule changes, will be a fresh start.
"I hope my experience will be useful in helping the team in its effort to move on from a difficult period," he said.
"I'm fully prepared to work with everyone at Grove to make sure we find the right direction. I'm highly motivated to start working hard from the very beginning in what is an exciting new challenge in my career."
On Sunday, Massa said farewell to thousands of Ferrari fans in Italy and received a trophy nearly as tall as him to celebrate his time with the team.
"I've been lucky, I have had a great career with Ferrari, longer than I had ever dreamed of at the start," the departing Brazilian told reporters after appearing at a wet Mugello track for a Ferrari event with a 15,000-strong crowd.
"When I began racing in go-karts as a kid, I had a red Ferrari suit and it's always been the team I supported. Even when Senna was at McLaren and Piquet at Williams, I was cheering for Ferrari."
"Felipe has been a true Ferrari man and he will always be part of our history," said Montezemolo. "I think the decision to go our separate ways is the right one, both for us and for him."