2010-11: Tyson Baillie played for the Boston Pizza Rangers midget AAA team in Fort Saskatchewan, Alberta and played for Team Alberta in the 2010 Canada Winter Games. Baillie was tied with Nicholas Lamoureux for second on the Rangers with 33 points in 33 games — scoring 12 goals with 21 assists and 66 penalty minutes. The Rangers finished fifth in the Dodge Division and Baillie scored 2 goals with 1 assist in three playoff games. In six games at the Canada Winter Games he scored 2 goals with 3 assists and 2 penalty minutes as Team Alberta won a bronze medal. Baillie was selected by Kelowna in the third round (53rd overall) of the 2011 WHL Bantam Draft.
2011-12: Baillie made his WHL debut as a 16-year-old — skating in 68 regular season and four playoff games for Kelowna in his first season — and played for Canada Pacific in the 2012 U17 World Hockey Challenge. Baillie scored 10 goals with 18 assists and was +11 with 33 penalty minutes for the Rockets. Kelowna finished third in the B.C. Division before being swept by WHL Finals-bound Portland in the first round. Ballie finished with an even plus/minus and 2 assists in 4 games against the Winterhawks. He scored 1 goal with 1 assist and had 10 penalty minutes in five games at the WHC.
2012-13: Baillie skated in 67 of 72 regular season games for Kelowna in his second WHL season. Playing on a Rockets team that was second to Portland in goals scored, he scored 26 goals with 30 assists and was +36 with 56 penalty minutes. The Rockets finished second in the B.C. Division and reached the second round in the playoffs. Baillie scored 8 goals with 6 assists and was +8 with 18 penalty minutes in nine playoff games.
2013-14: Baillie was named an assistant captain for Kelowna and skated in 56 of 72 games for the Rockets — missing the final 16 regular season games do to a lower leg injury — before returning for the playoffs. He scored 22 goals with 33 assists and was +19 with 53 penalty minutes as Kelowna finished first in the B.C. Division with a league-best 118 points. Baillie was ranked 90th amongst North American skaters in Central Scouting's mid-term rankings prior to the 2014 NHL Draft.