The 32-year-old found out he was dealt at the Flames' practice Sunday in Philadelphia.
"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.
Glencross has nine goals and 19 assists in 53 games this season for Calgary, which is three points out of the second wild-card spot in the Western Conference.
Flames general manager Brad Treliving said it was tough to trade Glencross, who played seven seasons in with the Flames and was active in the community in Calgary. But the return — two picks in the talent-rich 2015 draft — was too much to pass up.
"I think I've been consistent in talking about the need to continue to build our base," Treliving told reporters in Philadelphia. "To build our prospect base, to build the asset base, and I think this is a significant return. A second round- and third-round pick are good assets, and I think they're heightened in a draft like this."
Washington receives a hard-nosed veteran forward that can help the Capitals in their push towards the playoffs. Washington entered its home game Sunday night against Toronto holding down the top wild-card spot in the Eastern Conference.
"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. "We felt we needed to get deeper and more experienced at the forward position. Curtis plays important minutes and his presence on-and-off the ice will benefit our young forwards."
Glencross has a cap hit of US$2.55 million in the final year of his contract.
The third-rounder is Washington's, even though the Capitals also have Buffalo's pick from a 2014 trade.