Marek Vanacker was born in Delhi, Ontario, Canada and played youth hockey for the Brantford 99ers. In 2021-2022, Vanacker played in 23 games and recorded 19 goals and 26 assists. He was selected 23rd overall by the Brantford Bulldogs in the OHL Draft in 2022.
As a 16-year-old, he struggled in his first OHL season. He played in 55 games and recorded 4 goals and 12 assists for the Bulldogs. That summer he played in the U17 World Hockey Classic for Team Canada Black and had 3 assists in 7 games.
Last season was a different story for Vanacker. He led Brantford in scoring with 36 goals and 46 assists in 68 games and became a potential first round pick.