Fenerbahce announced the signing on Friday, but kept the contract length and transfer fee undisclosed.
Ake, 31, joined Manchester City from Bournemouth in 2020 for a reported fee of €45 million. The The Hague-born defender made 177 appearances for Manchester City across all competitions, winning 12 trophies along the way.
The multifunctional defender was active at the 2026 FIFA World Cup with the Netherlands, playing in three of Oranje's four World Cup games and starting against Morocco in the fateful round-of-32 matchup.
Ake joins Fenerbahce after the Istanbul giants failed to win the Turkish league for the twelfth consecutive season, this time finishing one point behind champions Galatasaray.
Fenerbahce fired manager Domenico Tedesco after one season and welcomed back Ismail Kartal for a fourth spell as manager.