In his second WHL season, 2012–13, Klimchuk improved to 76 points and finished second in team scoring. He made two appearances with the Canadian national under-18 team. He was a member of the gold medal-winning Canadian team at the 2012 Ivan Hlinka Memorial Tournament. Playing on the top line with Sam Reinhart and Connor McDavid, Klimchuk scored eight points to help lead Canada to a gold medal at the 2013 IIHF World U18 Championships.