2009-10: Brandon Alderson made his OHL debut as a 17-year-old and skated in 67 games for the Sarnia Sting. He scored 13 goals with 11 assists and was -17 with 30 penalty minutes. The Sting finished last in the West Division, winning a league-low 17 games. He was ranked 154th amongst North American skaters in Central Scouting's final rankings but was not selected in the 2010 NHL Draft.
2010-11: Alderson skated in all 68 games for Sarnia in his second OHL season despite playing with a wrist injury that required surgery in April. He scored 11 goals with 19 assists and was -20 with 63 penalty minutes. The Sting missed the playoffs for the second straight season; finishing fourth in the West Division.
2011-12: Obtained by Sault Ste. Marie in a June 2011 trade with Sarnia, Alderson played 65 games for the Greyounds in his third OHL season. He scored 17 goals with 22 assists and was +5 with 81 penalty minutes. Sault Ste. Marie came up just short in its quest for a playoff spot; finishing one point behind Windsor for the final spot in the Western Conference.
2012-13: Alderson signed a three-year entry-level contract with the Flyers in March 2013 and made his pro debut with Philadelphia's AHL affiliate in Adirondack following an over-age season in the OHL. He made his debut with the Phantoms in April and in nine games he had 2 assists and was an even plus/minus with 2 penalty minutes. Adirondack missed the playoffs after finishing last in the Northeast Division. Skating on a line with fellow Flyers prospect Nick Cousins in his second season with Sault Ste. Marie, Alderson scored 28 goals with 36 assists and was +13 with 64 penalty minutes. The Greyhounds finished second in the West Division and Alderson scored 1 goal with 3 assists and was +1 with 4 penalty minutes in four games in the first playoff series of his OHL career.
Alderson signed as a free agent by the Philadelphia Flyers in March, 2013. He will play for the AHL's Adirondack Phantoms in 2013-14.