Kökcü went through Olympia Haarlem, HFC EDO, Stormvogels, and Groningen before joining the youth ranks of Feyenoord in 2014. The midfielder made his debut for the Rotterdam club's first team at just 17 years old in a KNVB Cup match against VV Gemert, where he scored one of the goals in a 4-1 victory, played on September 17, 2018.
In the 2022/23 season, already as Feyenoord’s captain, Kökcü led his team to the Eredivisie title and was twice named Player of the Year—once by a jury of 35 Dutch internationals and also by the votes of the captains of the competing teams.
Eligible to represent both the Netherlands and Turkey, Kökcü chose to play for the Turkish national team after progressing through the Netherlands' U-17, U-18, and U-19 squads. He made his debut on September 6, 2020, in a UEFA Nations League match.
