Glencross, 32, is set to be an unrestricted free agent this summer.
“Curtis is a player we coveted and we are pleased that he decided to waive his no-trade clause to join our team,” Capitals general manager Brian MacLellan said in a statement released by the team. “We felt we needed to get deeper and more experienced at the forward position.
The Kindersley, Sask., native appeared in 418 contests over seven seasons with the Flames and ranks 26th all-time on the franchise games played list.
His most productive season in Calgary was in 2011-12 when he set career highs in goals (26) and points (48) while leading the NHL with a 23.6 shooting percentage.
“As tough as it is to say goodbye to everyone in Calgary and the fans — I’ve had such great support over the years — I’m excited for a new start,” Glencross told reporters in Philadelphia prior to joining his new team in Washington.?
Washington retains Buffalo’s third-round pick in this summer’s draft, acquired in a March 4, 2014 deal that sent goalie Michal Neuvirth and defenceman Rostislav Klesla to the Sabres for netminder Jaroslav Halak.