Samuelsson debuted for the Swedish national team at the 2005 World Championships in Austria. He recorded five points in nine games as Sweden finished in fourth place, losing the bronze medal game to Russia. The following year, he competed in the 2006 Winter Olympics in Turin. He contributed four points in eight games, while playing on a line with future Canucks teammates Henrik and Daniel Sedin. Samuelsson recorded an assist against Finland in the final, helping Sweden win gold. Later that year, he played for Sweden at the 2006 World Championships in Latvia, a tournament in which Sweden defeated the Czech Republic 4–0 in the final. Sweden became the first team in hockey history to win the Olympic gold and the World Championship in the same year. He recorded an international career-high nine points over eight games to tie for second in team scoring, while also leading Sweden in shots on goal.