Johnston won two gold medals with the National Women's Under-22 Team at the Air Canada Cup. Rebecca made her debut at the 2008 IIHF World Women's Championship, playing in all five games as Canada won silver. Rebecca Johnston was a member of Canada's Under-22 Team. The U-22 participated in the MLP Cup, held in Ravensburg, Germany from Jan. 2–6, 2009. Johnston was part of the silver medal winning team. In the tournament, Johnston accumulated seven points (3 goals, 4 assists). Her best game was in an 11–0 victory over Russia. Johnston scored a hat trick and added an assist. In addition to the MLP Cup, Johnston played with the Canadian Senior Team in the Four Nations Cup between Nov. 4–9, 2009. Johnston was part of the silver medal winning team. In the gold medal game of the 2010 Four Nations Cup, Rebecca Johnston's second goal of the game clinched the gold medal for Canada. Said goal came on a power play 6:21 into overtime. The goal gave Canada a 3–2 win over the United States. It was Hockey Canada's 12th championship in the tournament's 15-year history. She would lead all Canadian scorers in the tournament with four goals. In a game versus Russia at the 2012 IIHF Women's World Championship, Johnston registered a five-point game (one goal, four assists) in a 14–1 victory. In December 2013, Johnston was named to 2014 Olympic roster for Canada.