Smith skipped Scotland in three straight World Junior Curling Championships, earning a podium finish in each tournament. At the 2012 World Junior Curling Championships he led his team of Thomas Muirhead, Kyle Waddell, Kerr Drummond and Hammy McMillan Jr. to a bronze medal finish. The team finished the round robin with a 7-2 record, but went on to lose to Norway in the 3 vs. 4 playoff game. However, they avenged this loss in the bronze medal game when they defeated the same Norwegian team to finish third. At the 2013 World Junior Curling Championships, he led teammates Muirhead, Waddell, brother Cameron and McMillan to a gold medal. The team topped the round robin table with an 8-1 record, and would go on to defeat Canada and Russia (skipped by Evgeny Arkhipov) in the final to claim the championships. Later in the year, Smith led Great Britain to a silver medal at the 2013 Winter Universiade (representing Scottish Agricultural College). Smith with teammates Muirhead, Waddell, Cameron Smith and Derrick Sloan would lose in the final to Sweden's Oskar Eriksson. Later in the season, at the 2014 World Junior Curling Championships, Smith led Muirhead, Waddell, Cameron Smith and Duncan Menzies to a silver medal. The team would finish the round robin in a four-way tie for second place with a 6-3 record. They then defeated Norway in their first playoff match, sending them to the final, where they lost to Switzerland's Yannick Schwaller, settling for silver.