As per BBC Sport, City have finalised the deal for around £32 million and will look to the 23-year-old defender to fight for a first XI spot sooner rather than later, as their most expensive addition of the 2014 summer transfer window.
He's a signing City have clearly been chasing for some time and will not only bring great ability to the back line but also a depth that the side was missing at times last season, especially when club captain Vincent Kompany was missing from the line-up.
Belgian defender Kompany is rightly the defensive king at the Etihad Stadium after several seasons of top-class performances, but there were times last season when he seemingly had to hold the defence together himself.
Matija Nastasic suffered with injuries and inconsistency, Joleon Lescott was either not trusted or not wanted by manager Manuel Pellegrini, and although Martin Demichelis was not as bad as some would have you believe, he certainly has his limitations.
Mangala is expected to be Kompany's partner in defence, but his presence will also make sure there is still a top-class centre-back in the side for when the Belgian is absent, as he has struggled with injury himself at times, not to mention the odd suspension.
Strength in depth is key, and Mangala's arrival would mean City have two genuinely prime-level players in front of Joe Hart.
One of Mangala's main assets has to of course be his physicality.
Fast, powerful and dominant aerially, he looks set to be a complementary addition to the poise and the composure of Kompany.
New City signing Fernando has of course played at Porto with Mangala and states what he can bring, per Chris Wheeler of the Daily Mail: "I’ve played with him for a long time, he’s a great player and a friend as well. He’s very quick and strong, very competitive. He might bring a different element to the team that City doesn’t have, with his characteristics."
Mangala has shown great consistency for Porto, he has established himself as France's fourth-choice centre-back at the international level and has won titles in two smaller domestic leagues. He will now be aiming to do the same with City in England.
Best Back Line?
The signing of Mangala gives City four established central defenders and huge depth overall for the back four.
Kompany and Mangala, Nastasic and Demichelis—those four can certainly rival most or all Premier League centre-back options at each club, while in Pablo Zabaleta, Bacary Sagna, Gael Clichy and Aleksandar Kolarov they boast international full-backs, too.
Perhaps Chelsea, with the likes of Branislav Ivanovic, Gary Cahill, John Terry, Filipe Luis and Cesar Azpilicueta can claim to match them for a "best four," but City certainly have even better depth in their defensive area of the squad in every department.
As the season goes on, that might prove telling in individual games, but for the campaign as a whole, they will hope that Mangala and Kompany can forge a tight partnership which can lead them to another Premier League title.