The Foxes announced the Portugal full-back has signed a five-year-deal, having arrived on Saturday to finalise personal terms and complete a medical in a deal that could reach £21.9m ($29.4m).
Pereira's move will be ratified when transfer clearance is received on June 9 and the 24-year-old's immediate focus will be on Portugal's World Cup campaign.
"I feel very happy to be here and I can't wait to do my best to help the team," he told Leicester's official website.
"The atmosphere, the fans and the football of the Premier League makes it the best in the world. I am here to support the team and to help the club to achieve its goals."
Pereira is well known to Leicester boss Claude Puel, having played under the Frenchman during a loan spell at Nice.
1 - Amongst Portuguese Primeira Liga defenders in 2017-18, Ricardo Pereira ranked joint-first for tackles per 90 (3.9) and first for dribbles completed per 90 (1.9). Foxy. pic.twitter.com/oEXd2OJLrk— OptaJoe (@OptaJoe) May 19, 2018
Puel added: "I'm delighted to have a player of Ricardo's quality on board for next season. I remember him well from my time at Nice."
The Portugal international, who can also play on the wing, counts a Taca de Portugal medal with Vitoria Guimaraes and a Primeira Liga triumph with Porto this season among his list of achievements.