On June 17, 2010, the Blues acquired goaltender Jaroslav Halak from the Montreal Canadiens in exchange for prospects Lars Eller and Ian Schultz. Although he had yet to officially take over duties as GM, this was considered to be Armstrong’s first big move as the GM of the Blues.
Armstrong has been part of Hockey Canada's management group for the gold medal-winning teams in the 2010 and 2014 Winter Olympics; 2007 and 2016 Gold Medal World Championship Teams, 2016 World Cup Championship Winning Team plus the Silver Medal Winning Teams in the 2008 and 2009 World Championship. After winning the Stanley Cup in 2019 with the St. Louis Blues Armstrong became the 1st person in management to become part of the Double Triple Gold Club ( Winning Stanley Cup in 1999 and 2019, Olympics in 2010 and 2014 plus World Championship in 2007 and 2016). He also served on Canada's 2002 World Championship Team (did not medal).