The 27-year-old, who can also play as a right-back, has impressed with his consistent displays in La Liga over the past twelve months following his £7m switch from FC Porto this time last summer.
Integral for Valencia - how will he fare at City?
He was an integral part of Los Che's domestic success and constantly proved why he was one of the best defenders in the league at the time. He also won a place in the 2014/15 La Liga Team of the Season, which just highlights how good he was defensively in shutting out attackers with seeming ease.
The Argentine is now one of four in the first-team squad; Pablo Zabaleta, Martin Demichelis and talisman Sergio Agüero all featured alongside him at this summer's Copa América - where they came up short in the final to winners Chile on penalties.
A real signal of intent
City's main problem over the past few years has undoubtedly stemmed from their defensive issues, and signing Otamendi not only proves they are eager to mix it with the big boys in Europe - but they also want to regain the Premier League title too. Having already tied up deals to sign Fabian Delph and Raheem Sterling within the first-team, as well as Patrick Roberts within the youth system, this deal takes their spending for the summer window to just under £100million pounds.
Perhaps what makes this transfer signing even more sweet for City fans, is the fact that local rivals Manchester United were indeed in the running for the talented Argentine. They've been interested in him for months on end now, after rumours surrounding Real Madrid's Sergio Ramos cooled.
Praise in the highest order
His new manager, Manuel Pellegrini, said Otamendi was "arguably the best defender" in the league last season, so he's "naturally delighted to have added a player of his quality" within the ranks. He continued his praise, saying he's an "established international for one of the best nations in world football", and he has the "right mentality to fit into the squad" - where he'll link up with the likes of Eliaquim Mangala and Fernando, both of whom he played alongside at Porto.
Otamendi meanwhile said that he's here to "give my best", to "fight game-by-game" and in the same "push City to the highest peaks for as long as possible" - where he wishes he'll help the side to win several cups and titles in the process.