Stastny began his junior hockey career with the River City Lancers of the United States Hockey League before moving to the University of Denver Pioneers in 2004. He won the NCAA Men's Ice Hockey Championship in his first season playing for the Pioneers. He remained at the University of Denver for one more season. He signed a contract with the Avalanche before the 2006–07 NHL season, scored 78 points in 82 games in his rookie season and was nominated for the Calder Memorial Trophy. In 2007–08 he was named to his first NHL All-Star Game, but didn't play because of an appendectomy. As a dual citizen, Stastny has chosen to play for the U. S. in international hockey competitions, which have included the 2004 Viking Cup, the 2007 IIHF World Championship, and the 2010 and 2014 Winter Olympics.