Jackson, an electrifying playmaker, was cut loose by the Eagles last week amid concerns about his attitude and off-field activity.
The NFC East rival Redskins did not take long to lure him and will add him to an offense that features quarterback Robert Griffin III and NFL receptions leader Pierre Garcon.
Jackson reacted to the news by tweeting: "Its goin down!! Burgundy & Gold."
Terms of Jackson's contract have yet to be disclosed, according to the NFL's website.
The 27-year-old Jackson is coming off a career-best season that saw him catch 82 passes for 1,332 yards and nine touchdowns.
(Writing by Jahmal Corner in Los Angeles; editing by Sudipto Ganguly)