Pep Guardiola has been in search of another centre-back since Vincent Kompany's departure last May.
Aymeric Laporte endured an injury hit campaign in 2019-1920, though the Frenchman was a regular after the restart of the Premier League season in June, while doubts remain over the futures of John Stones and Nicolas Otamendi.
Youngster Eric Garcia put in some impressive displays towards the end of the season, but City – which hasalso been linked with Napoli star Kalidou Koulibaly – has moved to bolster its defensive ranks, with Ake joining from relegated Bournemouth.
The 25 year-old Netherlands international, who Bournemouth signed permanently from Chelsea for £20m in 2017, has penned a five-year contract at the Etihad Stadium.
"City have been the best side in England over the course of the last decade," Ake said. "Coming here is a dream for me. This is a top side full of world-class players. Everywhere you look in this squad there are big names with international pedigree.
"Pep is a manager admired across the world – what he’s done in the game speaks for itself. The success he’s had is unbelievable and the style of football he plays really appeals to me.
"I know I’m going to have to work hard to get into the side, but that’s what I’m here to do. I’ll do whatever I can to make an impact and help the team win silverware."
After featuring in every Premier League match for the Cherries in 2017-2018 and 2018-2019, injury restricted Ake to 29 league appearances last season as Eddie Howe's side dropped out of the top flight.