2009-10: Mark Simpson skated in three games for Saint John Vito's midget AAA team in New Brunswick — with no points nor penalties — and was the leading scorer for the K.V. Rangers bantam team.
2010-11: Simpson had 12 points in 19 games with Saint John Vito's midget AAA team as a 15-year-old and was the second-leading scorer for the Kenn Valley Spartans U16 team despite appearing in only 19 of 30 games. He scored 1 goal with 9 assists and 6 penalty minutes in 14 regular season games and had 2 assists in five playoff games for Vito's. Simpson scored 10 goals with 27 assists and had 10 penalty minutes with the Spartans.
2011-12: Simpson appeared in one game with the junior A Woodstock Slammers and was the leading scorer for Saint John Vito's; finishing tenth in the NBPEI midget AAA league in scoring. He had no points nor penalties with the Slammers. Simpson scored 14 goals with 29 assists and 22 penalty minutes in 33 regular season games for Saint John and had 1 goal and 6 penalty minutes in four playoff games. He was selected by Moncton in the ninth round (155th overall) of the 2012 QMJHL Entry Draft.
2012-13: Simpson skated in four QMJHL with Moncton and was the sixth-leading scorer for the Dieppe Commandos of the Maritimes Junior A Hockey League. He was -1 with no points nor penalty minutes for the Wildcats. Simpson scored 21 goals with 25 assists and 18 penalty minutes in 51 regular season games for Dieppe and scored 3 goals with 5 assists and no penalties in five playoff games. Simpson was not among the 210 North American skaters in Central Scouting's final rankings and was not selected in the 2013 NHL Draft.
2013-14: Simpson made Moncton out of training camp and appeared in 44 games in an injury-filled campaign. After missing over two months, he returned to the Wildcats lineup at the end of February and for the season he scored 8 goals with 12 assists and was an even plus-minus with 23 penalty minutes. The Wildcats finished third in the Maritimes Division and lost to Blainville-Boisbriand in a first round series. Simpson had no points nor penalties and was -6 in six playoff games. He appeared in Central Scouting's mid-term rankings (172nd amongst North American skaters) but was not among the 210 players listed in the final rankings prior to the 2014 NHL Draft.