The 23-year-old centre-back has signed a six-year contract, which keeps him at the Club until the summer of 2026.
Dias has made more than 100 appearances in three seasons for the Lisbon giants, with whom he won a league title in 2018/19 and has been capped 19 times by Portugal.
Having developed a reputation as one of the most promising defenders in Europe, he says moving to City was an easy decision as he feels he is joining a club where he can improve and be successful.
“To have the opportunity to join a club like Manchester City is a fantastic opportunity for me and one I couldn’t turn down," he said.
“Their success speaks for itself. They have been the dominant team in England over the last few years, playing an attacking brand of football which I feel suits my own game.
“It is really exciting to be part of such a talented squad and to play for a world class manager like Pep Guardiola, who has a proven track record of developing young players like myself.
“I believe I can improve here, at a club whose ambitions match my own and I will give everything to be successful and win titles.”
Director of Football, Txiki Begiristain, added: “Ruben is a player we have admired for some time and we have been impressed with how he has progressed at Benfica.
“He has developed into a real leader and as a defender, he has all the attributes we are looking for. He is strong in the air, good in one v one situations and technically, he is very good, so we are confident he can thrive in our system.
“He is young, but has experience playing for a top European club in Benfica and we’re really pleased we’ve been able to sign him.
“He is another talented addition to the squad and someone who is only going to get better working under Pep.”
A product of the famed Benfica academy, which also developed new team-mates and compatriots Bernardo Silva and Joao Cancelo, Dias has already achieved a lot in his short career.
Having helped the Eagles’ U19 team to the final of the UEFA Youth League in 2016/17, he made his first team debut in a 2-1 defeat to Boavista in September 2017 and went on to make 29 appearances that season.
He was voted the Primeira Liga's best young player in 2017/18 and in the following campaign, he truly established himself at the heart defence, playing 55 times in all competitions and helping Benfica to a 37th league title.
Last season, Dias made 49 appearances and scored three goals as he was named in the Primeira Liga Team of the Season.
The defender has also won team and individual honours at international level.
Having made his Portugal debut against Tunisia in May 2018, he was an unused member of the squad at the 2018 World Cup in Russia, but 12 months later he proved instrumental in his country’s UEFA Nations League triumph.
The youngster played the full 90 minutes in the last four against Switzerland and in the 1-0 win over the Netherlands in the final, where he was named Man of the Match and included in the Team of the Tournament.
Everyone at Manchester City is pleased to welcome Ruben to the Club and wishes him the best of luck during his time with us.
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