Ricardo, 24, arrived in Leicester on Saturday to finalise personal terms on a five-year contract and complete a medical.
His move to City will be complete when international transfer clearance is received on 9 June.
He will report for international duty this week, having been named alongside Adrien Silva in Portugal's 23-man squad for this summer's World Cup in Russia.
The 24-year-old right-back, who can also operate as a winger, made 43 appearances for Porto in all competitions this season, including seven in the UEFA Champions League, and helped the side to their 28th Portuguese league title this month.
He told LCFC TV: “I feel very happy to be here and I can't wait to do my best to help the team. 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."