Porto announced to the Portuguese stock exchange on Wednesday that the deal had been agreed and now confirmation has come via City themselves.
Fernando, 26, will wear the No. 6 shirt at City next season and could form a formidable midfield triumvirate with Fernandinho and Yaya Toure.
The midfielder, who won four league titles, two Portuguese cups and the Europa League with Porto, told City's official website: "I am so happy to finally be joining Manchester City. I know there was talk of me possibly signing last January so I am delighted that the deal has now been done and that I am a City player.
"I’m looking forward to meeting my new team-mates and helping City to defend the title. It is a very exciting time to be part of this football club and I cannot wait to play in the Premier League. City fans can be assured I will give my all every time I play and I’m looking forward to many happy years in Manchester.
"I have enjoyed my stay with Porto and I thank the club and the fans for their support during my time in Portugal. Now I am ready for a new chapter in my career.”
Fernando signed for Porto from Vila Nova in 2007 and has represented Brazil at youth level. He won the treble under Andre Villas-Boas in 2011, anchoring the midfield.
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