The Wizards are Harrington's seventh NBA team as he enters his 16th season. He's averaged 13.7 points and 5.7 rebounds in 947 career games.
Harrington played in only 10 games with the Orlando Magic last season because of a right knee injury.
Via Twitter, Harrington recently proclaimed himself to be "almost 110% back healthy" after a harrowing run of ill health stemming from a staph infection he contracted after surgery to repair a torn meniscus in his right knee in April 2012.
Since the regular season ended, Harrington has been working all summer in Las Vegas with noted NBA trainer Joe Abunassar at the Impact Academy and reportedly attracted interest from multiple teams -- including Chicago and the Los Angeles Clippers -- before zeroing in on Washington.
Wizards president Ernie Grunfeld said Wednesday that Harrington will give the team additional depth in the frontcourt.
Information from ESPN.com's Marc Stein and The Associated Press was used in this report.