Nkoudou, who joined Spurs from Marseille in 2016, had earlier bid farewell to Tottenham in a social media post that thanked the club for his three years with them.
It's great to see you at Beşiktaş https://t.co/gvJoXx7Szs— Beşiktaş JK (@Besiktas) August 22, 2019
The former France Under-21 winger has signed a four-year contract with Besiktas that promises to keep him in Istanbul until the summer of 2023.
Now 24 years of age, he will have the opportunity to kickstart his career in Turkey after it had stalled in north London. Nkoudou was ultimately unable to establish himself as a Spurs regular and spent each of the last two seasons out on loan, first with Burnley then Monaco.
Nkoudou played only 26 games for Spurs. Only 10 of those appearances were in the Premier League, with the rest in domestic and European cup competitions.
A statement from Spurs read, “We wish 'GK' all the best for the future.”
He is one many players who have left the club since the end of last season, including Kieran Trippier, Vincent Janssen, Fernando Llorente and Josh Onomah. He is Besiktas’ fifth permanent signing of the summer after Adem Ljajic, Tyler Bord, Douglas and Victor Ruiz.