The 38-year-old American scored 18 goals with 176 assists.
“I’ve been extremely lucky to have the best job in the world for many years, but my body is telling me it is time to move on to something new,” Orpik said in a statement released by the NHLPA.
Orpik played 10 seasons with the Pittsburgh Penguins before joining the Capitals as an unrestricted free agent.
He won two Stanley Cups, Pittsburgh in 2009 and the Capitals in 2018, the first in Washington’s history.
“Not only was he a great leader and a player, but he was a better person,” Capitals captain Alex Ovechkin said. “I’m so happy I had a chance to play with him and for our young guys to have had the chance to learn from him. I want to wish him, Erin and his kids the best. We will miss him and the Batya protein shakes!”
Orpik also played on two United States Olympic teams in 2010 (silver medal) and 2014.