2010-11: Julius Vahatalo skated for the TuTo club in Turku, Finland; splitting the season between the U18 and U16 teams. In 27 games at the U18 level he scored 4 goals with 9 assists and 35 penalty minutes. Vahatalo played 19 games with the TuTo U16 team, including two C junior playoff games, and scored 31 goals with 29 assists and 6 penalty minutes.
2011-12: Vahatalo started the year with TuTo before skating for Turku top division club, TPS. He played eight games in A junior with the TPS U20 team, recording 1 goal with 1 assist and finishing with an even plus/minus. He played a key role for the TPS U18 team as the squad captured a bronze medal in the B junior playoffs. Vahatalo scored 5 goals with 12 assists and 14 penalty minutes in 17 regular season games and scored 2 goals with 4 assists in six playoff games. In 11 games with TuTo’s two B junior teams he scored 4 goals with 3 assists and 6 penalty minutes.
2012-13: Vahatalo skated in eight games with the TPS U20 team and played 14 games for the TPS U18 team — missing nearly three months after suffering a hand injury when he was cut by a skate. He had 4 assists and was +2 with 2 penalty minutes for TPS in A junior play. He scored 11 goals with 13 assists and 8 penalty minutes in 13 regular season games for the TPS U18 team and had 2 assists in one playoff game.
2013-14: Vahatalo made his Liiga debut in January, skating in 18 regular season games for TPS, and was the second-leading scorer for the TPS U20 team despite skating in just 33 games during the regular season. He recorded 3 assists and was +1 with no penalties, averaging eight minutes of ice time with the TPS men’s team. Vahatalo scored 18 goals with 21 assists and was +20 with 6 penalty minutes in the regular season for TPS in the A junior regular season and was minus-1 with no points nor penalties in three playoff games. Not among the 140 international skaters in the Central Scouting rankings in his second year of draft eligibility, Vahatalo was selected by Detroit in the sixth round (166th overall) of the 2014 NHL Draft.