Julius Miettinen was born in Helsinki, Finland and played for the HIFK U18 team in 2021-2022. In 25 games, he collected 9 goals and 11 assists. The following season he played on the HIFK U20 team and tallied 10 goals and 12 assists in 38 games. He also played in 26 International games during the 2022-2023 season and scored 7 goals and 1 assist. Miettinen was selected 30th overall in the CHL import draft by the Everett Silvertips of the WHL.
In his first season in the WHL, Miettinen did not disappoint. He played in 66 games and averaged over a point a game, scoring 31 goals and 36 assists. He enters his draft year as one of the top rated Finnish players.