[2] Following his selection by the Toronto Maple Leafs of the National Hockey League (NHL) in the third-round, 84th overall, in the 2019 NHL Entry Draft, Kokkonen continued his development with Jukurit, appearing in 39 regular season games and collected 3 goals and 10 points in the 2019–20 season.
In his fifth year in the Liiga during the 2020–21 season, Kokkonen was selected as an alternate captain for Jukurit.
[3] On 31 March 2022, the Toronto Maple Leafs announced they had signed Kokkonen to a three-year, entry-level contract, beginning in the 2022–23 season.
[5] For the 2022–23 season Kokkonen was assigned first to the Marlies, and then to Toronto's ECHL affiliate, the Newfoundland Growlers.
[7] Kokkonen represented Finland at two World Junior Championships; the first in 2020 and the second in 2021, winning the bronze medal in the latter.