2008-09: Brett Ritchie played for the Toronto Marlboros in the GTHL. Chosen in the first round, 12th overall, of the 2009 OHL Priority Selection by the Sarnia Sting.
2009-10: In his OHL rookie season, Ritchie played in 65 games for the Sting. He scored 13 goals and 16 assists for 29 points. Ritchie played for Team Ontario at the 2010 World U-17 Hockey Challenge, scoring 2 goals and adding 1 assist for 3 points in 6 games.
2010-11: In 49 games for the Sting, Ritchie scored 21 goals and added 20 assists for 41 points to go along with 47 penalty minutes. Ritchie played for Canada at the 2011 U-18 World Junior Championship, scoring 4 goals and adding 3 assists for 7 points in 7 games.
2011-12: Ritchie returned to Sarnia for a third season in the OHL after attending Stars camp. After scuffling a bit with the middle-of-the pack Sting, and missing ten games with a hip injury Ritchie's offensive production picked up following a trade to powerful Niagara in early January. He scored 8 goals with 7 assists and was an even plus/minus with 30 penalty minutes in 23 games with Sarnia. Joining the powerful Ice Dogs, which finished first in the Central Division and featured a handful of high draft picks, Ritchie scored at a point-per-game pace – finishing with 16 goals and 40 assists in 30 games with a plus-27 plus/minus and 24 penalty minutes. Niagara reached the OHL finals and Ritchie scored 3 goals with 8 assists and was an even plus/minus with 16 penalty minutes in 20 playoff contests. He scored all three of his playoff goals on the power play.
2012-13: Ritchie made his pro hockey debut as a 19-year-old, joining Dallas AHL affiliate Texas following the OHL playoffs, and played for Canada in the 2013 World Junior Championship. In five regular season AHL games he scored 3 goals with 1 assist and was +3. The Texas Stars finished first in the South Division and reached the second round in the playoffs. Ritchie played in nine playoff games and was -2 with 2 goals and 2 penalty minutes. He was an assistant captain and the second leading scorer for Niagara in his first full season with the IceDogs. He scored 41 goals with 35 assists and was +35 with 40 penalty minutes in 53 games. Niagara lost to Oshawa in five games in a first round series after finishing fourth in the Central Division. In four playoff games Ritchie scored 1 goal with 3 assists. He played six games for fourth-place Canada at the WJC and was +3 with 1 goal and 3 assists. Canada lost to host Russia in the bronze medal game.
Big winger that moves well and has very good offensive instincts. Can use his body effectively when he has the puck on his stick. Has a good shot that can sneak up on goaltenders. Sort of a Jekyll and Hyde type player in his young career due to injuries. The dedicated Ritchie can be a force at both ends and exhibit big physicality and quality puck control. The casual Ritchie can often disappear for long stretches and stick to the edges of the rink. If his determination and work rate stay as high as they were during the second half of the 2010-11 season, Ritchie could be a fairly dominant player – otherwise, he could be a fairly dormant player.