Ivan Demidov was born in Sergiyev Posad, Russia. In the Russian Junior League (MHL), Demidov scored over 1.4 points per game, leading the league in scoring. Demidov won a gold medal with Team Russia at the 2021 Hlinka Gretzky Cup, scoring five points in 5 games. He made his professional debut shortly after with SKA Saint Petersburg of the Kontinental Hockey League at age 16.
Demidov, while playing for the SKA-1946 team in the MHL this past season, put up huge numbers, scoring 2 points a game, finishing with 23 goals and 37 assists in only 30 games.