2010-11: Ryan MacInnis attended USA Hockey's Select 14 Festival before returning to his native St. Louis to skate for the Junior Blues bantam AAA team.
2011-12: MacInnis played for the St. Louis Blues U16 midget team and was part of the USA U16 team at the 2012 Winter Youth Olympic Games. He scored 27 goals with 20 assists and had 18 penalty minutes in 34 games for the Blues. MacInnis was one of three players to finish with a team-leading six points for the USA at the WYOG tournament. He scored 4 goals with 2 assists and had 4 penalty minutes as the USA finished fourth. MacInnis was invited to USA Hockey's National Team Development Program evaluation camp in the spring; earning a spot at the NTDP for 2012-13. He was selected by Kitchener in the third round (46th overall) of the 2012 OHL Priority Draft.
2012-13: MacInnis joined USA Hockey's NTDP in Ann Arbor, MI, skating for both the U18 and U17 teams. MacInnis appeared in seven games with the U18 squad and had 2 assists. He was the third-leading goal scorer for the U17 team; finishing with 15 goals, 10 assists, and 6 penalty minutes in 52 games. The NTDP U17 team finished first in the 2012 Four Nations Tournament in Switzerland, third at the 2013 World Hockey Challenge, and third at the 2013 Five Nations Tournament in Finland. MacInnis scored 2 goals with 3 assists in six games at the WHC.
2013-14: MacInnis signed with the Kitchener Rangers in August 2013; foregoing his second year in the NTDP. MacInnis played in the 2013 CCM/USA Hockey All-American Prospects Game and was selected for Team Cherry in the 2014 CHL/NHL Top Prospects Game.