Stoch joins Fenerbahce from Chelsea
Stoch, in South Africa preparing for Slovakia's first appearance at a World Cup, joined Premier League Chelsea in 2006 as a 16-year-old.
He made five appearances for the Londoners as a substitute before going on loan to Twente Enschede this season and helping them win the Dutch championship.
The clubs, who announced the move on their websites did not give details of the fee.
Stoch is expected to be one of the key players for Slovakia at the World Cup. They are drawn in Group F with New Zealand, Italy and Paraguay.