The Portugal defender has extended and improved his deal to 2029.
“I am incredibly happy today,” the 28-year-old said.
“I’m so proud to represent this great Club. City are where I want to be – at the top of the sport, competing for trophies. The club’s ambition aligns perfectly with mine and as a footballer there is nothing better than that.
“I love Manchester – it is my home now – and I love the Manchester City fans. Their support from day one has been absolutely unbelievable, and I appreciate them a lot.
“When I think about the trophies we have won and the way we have played our football during my time here, I couldn’t imagine playing anywhere else.
“My job now is to be the best I can be for the duration of this contract, so that I can play my part in helping us challenge for more silverware.
“I want to thank my teammates, Pep, Hugo, the coaching staff and everyone at the Club. This is such a special place, and I am grateful every single day for the support I receive.
“Now the hard work begins, and I want to promise the fans that I will give everything to win more trophies and bring more success to City.”
Exciting development
Dias is now entering his fifth year with City, having arrived in 2020 from Benfica.
City's Director of Football Hugo Viana added: “As a club, we’re really excited that Ruben has signed a new contract and committed his long-term future to the Club.
“His hard work, professionalism and sheer dedication are clear to all of us every single day, He is a leader in the dressing room and on the pitch. He is one of our captains, the players listen to him and Pep and the coaching staff love working with him. He is the ultimate professional.
“His performances over the past five years have been outstanding and he is a big reason why we have been so successful. Every time Ruben pulls on a City shirt, he gives his all for the badge and we are so happy to know he will be here for the next four years.”