Undrafted, Halpern began his NHL career in the
1999–2000 NHL season for the
Washington Capitals. He played in 79 games, scoring 18 goals with 11 assists, and was +21. He was the first member of the Capitals to be born and raised in the
Washington, D.C. area. The
2003–04 NHL season was his highest-scoring season in the NHL, finishing with 46 points with 19 goals and 27 assists in 79 games. During the
2004–05 NHL lockout, Halpern played for the
Kloten Flyers and for
HC Ajoie in Switzerland, and returned to the Capitals when the lockout ended. On September 23, 2005, the Washington Capitals named Halpern the twelfth team captain in franchise history. In the
2005–06 NHL season, he scored 11 goals, and added a career-high 33 assists. On July 5, 2006, Halpern left the Capitals as a
free agent and signed a four-year deal with the
Dallas Stars. On February 26, 2008, Halpern was dealt to the Tampa Bay Lightning along with
Mike Smith,
Jussi Jokinen, and a 2009 4th-round draft pick in exchange for
Brad Richards and
Johan Holmqvist. Halpern scored a goal in his Lightning debut, and added an assist. After being acquired by the Lightning, Halpern went on a huge hot streak, scoring 10 goals and 18 points in 19 games. He also led the league during the
2007–08 NHL season in games played as one of only two players to appear in 83 games, or one more than a team's full schedule, as a result of his trade to Tampa Bay. The other was
Brian Campbell. Playing in 52 games during the
2008-09 NHL Season, Halpern scored seven goals to go with nine assists. . Halpern was named the captain of the
United States national team for the 2008 World Championships in Canada. Playing in a 5–4 loss in the opening round against the Canadian team on May 6, 2008, he suffered a ruptured anterior cruciate ligament and was expected to be out of action for 6–8 months. This occurred in the same game where USA goaltender
Tim Thomas was injured and had to leave the team. Halpern was traded from the Lightning to the
Los Angeles Kings March 3, 2010, in exchange for
Teddy Purcell and a 3rd round draft pick in 2010. On September 7, 2010, Halpern signed a one-year contract with the
Montreal Canadiens. He signed a one-year contract worth $825,000 to return to his original team the Washington Capitals on July 1, 2011. On July 9, 2012, once again as a veteran free agent, Halpern was signed to a one-year deal with the
New York Rangers. With the
2012–13 season delayed due to the
lockout, Halpern made his debut with the Rangers in the shortened season opener on the fourth line in a defeat against the
Boston Bruins on January 19, 2013. In 30 games with the Rangers as a checking line forward, Halpern produced one assist before he was claimed off waivers to return to the Montreal Canadiens on March 23, 2013. For the season, he had a goal and two assists in 46 games for the Rangers and Canadiens. In 13 NHL seasons at that point he had 147 goals and 214 assists (361 points) in 907 regular-season games. He also had seven goals and 14 points in 39 Stanley Cup playoff games. His contract included an NHL-clause. With the team, he scored four goals in eight games. On October 12, 2013. Halpern left the Finnish team and signed a one-year, two-way contract with the
Phoenix Coyotes. It would pay him $600,000 in the NHL, and $75,000 in the
AHL. ==Coaching career==