2009-10: Nathan Walker played four games with the Sydney Ice Dogs men’s team in his native Australia and spent his second full season playing junior hockey in the Czech Republic. He had one assist and no penalty minutes with the Ice Dogs. In 24 games with the HC Vitkovice U20 team, including one playoff contest, he scored 5 goals with 5 assists and was +1 with 16 penalty minutes. Walker was the third-leading scorer for the HC Vitkovice U18 team while playing in just 28 of 48 games. He scored 22 goals with 20 assists and was +25 with 47 penalty minutes. He scored 2 goals with 2 assists and was +3 with 4 penalty minutes in two playoff games.
2010-11: Walker appeared in three games for Sydney and played for the Australia men’s team in the 2011 Division 2A World Championship while spending most of the winter with HC Vitkovice. He scored 1 goal with 1 assist and 6 penalty minutes in three games for Sydney . Walker scored 4 goals with 2 assists and was +7 with 4 penalty minutes as Australia, the host team, won all four of its games to capture a gold medal. Walker was the third-leading goal scorer with 20 goals in 37 regular season games for the HC Vitkovice U20 team and was +40 with 22 assists and 20 penalty minutes. In ten games for the HC Vitkovice U18 team he scored 4 goals with 10 assists and was +12 with 22 penalty minutes.
2011-12: Walker played in the Czech Extraliga as a 17-year-old and played for Australia in the 2012 Division 1B World Championship. In 35 games with the HC Vitkovice men’s team, including one playoff game, he scored 4 goals with 5 assists and was minus-8 with 10 penalty minutes. He also played two games for HC Olomouc in the Czech second league and had 1 assist and 4 penalty minutes. Walker scored 2 goals and was minus-4 with 4 penalty minutes in five games for the Australia national team. In 17 games for the HC Vitkovice U20 team, including three playoff games, he scored 14 goals with 7 assists and was +12 with 16 penalty minutes. Walker was ranked 25th amongst International skaters in the Central Scouting final rankings prior to the 2012 NHL Draft but was not selected.
2012-13: Walker attended the Washington Capitals development camp prior to returning to the Czech Republic and split the first half of the season between the HC Vitkovice men’s and U20 teams. In January he headed to North America to skate in the USHL with the Youngstown Phantoms. Walker had 1 assist and was minus-2 with 29 penalty minutes in 20 Czech Extraliga games. He was an assistant captain for the HC Vitkovice U20 squad and in 13 games scored 12 goals with 12 assists and was +10 with 42 penalty minutes before joining the Phantoms. In 29 USHL games he scored 7 goals with 20 assists and was +5 with 63 penalty minutes before suffering a season-ending neck injury in April. Youngstown finished third in the Eastern Conference and reached the second round in the playoffs.
2013-14: Walker was invited to Washington’s training camp and signed an AHL contract with the Capitals affiliate Hershey. The youngest player in the league, he scored 5 goals with 6 assists and was minus-3 with 40 penalty minutes in 43 regular season games. The Bears finished fourth in the East Division; two points behind Norfolk for the final playoff spot. Walker was selected by Washington in the third round (89th overall) in the 2014 NHL Draft.