The 38-year-old American scored 18 goals and had 176 assists during his career.
"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 NHL Players' Association.
Orpik played 10 seasons with the Pittsburgh Penguins before joining the Capitals as an unrestricted free agent. Orpik was more known for his physicality and defense than his offense, but he scored the Game 2-winning goal for Washington in the 2018 Final while on the way to the franchise's first title.
He won two Stanley Cups, with Pittsburgh in 2009 and with the Capitals in 2018. He will be remembered for being the muscle behind the two Cup champions -- the first titles for Sidney Crosby and Alex Ovechkin. He often toed the line on hits and was suspended three games during the 2016 playoffs for a late, high hit that injured Pittsburgh's Olli Maatta.
"Not only was he a great leader and a player, but he was a better person," Ovechkin said in a statement released by the Capitals. "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.
The Associated Press contributed to this report.