Born in Canada to a Canadian mother and an American father, Sydney came up through the Canadian system and represented Canada at various youth levels, until she chose to play for the United States women's national under-20 soccer team starting in 2008 and later began playing for the U.S. senior national team in 2012. Leroux has earned over 75 caps with the senior national team and was part of the Americans' winning squads at the 2012 London Olympics and 2015 Women's World Cup.