The agreement, signed by Griffin Wednesday, is reportedly a four-year deal worth about $21 million. He was expected to join the team's rookie camp, which began Monday.
"Well people ... It's Time to go to Work!!!" Griffin posted Wednesday on his Twitter account. "Off the unemployment line and oh yea #HTTR!!!!"
"HTTR" refers to "Hail to the Redskins," the team's fight song.
Griffin won the Heisman Trophy in 2011 after helping Baylor to a 10-3 record and season-ending No. 12 ranking. Griffin passed for 4,293 yards and 37 touchdowns with six interceptions last season. He also rushed for 699 yards and 10 touchdowns.
He started 11 of 12 games in 2008, his freshman year at Baylor, but injured his knee and missed almost all of the 2009 season. He was the Bears' starting quarterback in 2010 and '11.
For his career, Griffin completed 776-of-1,159 passes for 10,071 yards and 78 touchdowns. He rushed 510 times for a total of 2,199 yards and 32 touchdowns.