The transfer is structured as an initial £21.4m with a further £4.3m in potential add-ons, and arrives as Bournemouth's response to losing Marcos Senesi, who left for Tottenham Hotspur on a free transfer earlier this summer.
Silva progressed through Benfica's academy at Seixal and racked up 235 senior appearances after his 2022 breakthrough, a run that brought six major honours including Portugal's 2025 Nations League triumph, and saw him named the Primeira Liga's Defender of the Year for the 2022-23 campaign — remarkable recognition for a player who had scored his first Champions League goal at just 18.
International recognition followed quickly too: 20 caps for Portugal by the age of 22, spanning the 2022 World Cup — where he featured as a teenager — and Euro 2024, though Roberto Martinez left him out of this summer's World Cup squad. He had just a year remaining on his Benfica contract and turned down the offer of a renewal, prompting the Portuguese club to cash in now rather than risk losing him for nothing next summer.
AFC Bournemouth president of football operations Tiago Pinto said the club had tracked Silva for some time.
"Antonio is a player we have admired for a long time and we're delighted to welcome him to AFC Bournemouth," he said. "Despite being only 22, he has already built an outstanding level of experience at one of Europe's biggest clubs, playing consistently in domestic, European and international competitions.
"Those experiences have helped shape him into a defender with real maturity and leadership qualities. He is ambitious, has a proven winning mentality and knows what it takes to compete for trophies. Those are the characteristics we want to bring into this football club as we continue to build a squad capable of competing at the highest level.
"We're excited to see Antonio continue his development here under Marco Rose and we're confident he'll be an excellent addition to the group."
Silva himself said he was relishing the move to the south coast.
"I am very happy to be here. It's a pleasure to play for Bournemouth and in the Premier League. I can't wait to start the season with my teammates and I'm excited to be here," he said. "The mentality is always to win. I will try my best, and I will play for the fans. We have everything here that helps us perform on the pitch, and I can't wait to get started."
Silva becomes Bournemouth's second signing of the week following the arrival of Elche forward Alvaro Rodriguez, with the club having conceded 54 goals last season and identifying central defence as a clear priority heading into the new campaign.