2009-10: Adam Tambellini played for the South Side Athletic Club Bulldogs minor midget AAA team in Edmonton. In 34 games he scored 27 goals with 24 assists and had 20 penalty minutes. The Bulldogs finished first in the North Division and in six playoff games Tambellini scored 6 goals with 4 assists and had 10 penalty minutes.
2010-11: Tambellini made his junior hockey debut, playing for the Albert Junior Hockey League's Sherwood Park Crusaders ,and was the second-leading scorer for the SSAC Boston Pizza Athletics in the Alberta Midget Hockey League. He scored 1 goal in three games with the Crusaders. Tambellini scored 22 goals with 25 assists in 33 games for the Athletics and had 4 goals with 2 assists in five playoff games as the first place Athletics were upset by the Sherwood Park Kings.
2011-12: Tambellini skated for the BCHL's Vernon Vipers in his first season of junior hockey and committed to playing college hockey at North Dakota in 2012-13. He was the third-leading scorer for the Vipers, finishing the year with 27 goals and 29 assists in 55 games with 28 penalty minutes. The Vipers missed the BCHL playoffs; finishing fifth in the Interior Division.
2012-13: Tambellini finished the season with BCHL champion Surrey after being obtained in January in a trade deadline deal with Vernon. He was the Vipers' leading scorer at the time of the trade – scoring 22 goals with 17 assists in 36 games – and had 14 goals and 13 assists in 16 regular season games with Surrey. He led the Eagles with 10 goals in 17 playoff games and had 8 assists with 6 penalty minutes. Surrey beat the defending champion Penticton Vees in six games in the BCHL finals. Ranked 62nd amongst North American skaters in Central Scouting's mid-term rankings, Tambellini was ranked 42nd in the final rankings prior to the 2013 NHL Draft.