Griffin's agent, Ben Dogra, told The Associated Press that the Heisman Trophy-winning quarterback agreed to terms and will be in Redskins rookie camp on Wednesday.
Griffin, the second overall pick in the draft out of Baylor, announced the news on Twitter, writing, "Well people....It's Time to go to Work!!! Off the unemployment line and oh yea HTTR!!!"
The latter stands for "Hail To The Redskins," the team's fight song.
Griffin will be on the field Wednesday for the third day of a five-day rookie camp. He wasn't considered a holdout because training camp doesn't officially begin until July 26.
The Redskins traded their first-round choices in 2012, 2013 and 2014 as well as their second-round pick this year to the St. Louis Rams on March 10 for the right to move up four spots to take Griffin.
Coach Mike Shanahan orchestrated the trade for Griffin, who threw for 4,293 yards and 37 touchdowns with just six interceptions and ran for 699 yards and 10 touchdowns in 2011 while leading Baylor to the Alamo Bowl.
Shanahan selected the 22-year-old Griffin the starter ahead of Grossman on the final day of rookie minicamp in May.
Washington made the big move after finishing last in the NFC East for a fourth straight year with a 5-11 record in 2011. That was the 16th season in the past 19 in which the Redskins didn't make the playoffs. During that span, they have started 21 quarterbacks. The most recent, Rex Grossman, committed 25 turnovers in 13 starts last season.
A few hours later, offensive lineman Josh LeRibeus, Washington's third-round choice, became the last of the Redskins' picks to sign.
Terms of the deal for the rookie from SMU were not disclosed.