Humphries appeared in 69 games, averaging 8.4 points and 5.9 rebounds, last season with Boston.
In 10 seasons with the Jazz, Raptors, Mavericks, Nets and Celtics, he is averaging 6.8 points and 5.5 rebounds.
Humphries had his best season in 2011-12 when he averaged 13.8 points and 11.0 rebounds for the Nets. He was selected with the 14th pick in the 2004 draft by the Jazz out of Minnesota.
Wizards President Ernie Grunfeld said over the weekend that "Kris is a proven veteran and will be a versatile addition to our front-court."
Humphries was previously married to reality TV star Kim Kardashian.
On Friday, the Wizards re-signed forward Drew Gooden.