Culliver and former Denver Broncos defensive tackle Terrance Knighton both signed their free-agent contracts with Washington on Friday, the same day the Redskins found out linebacker Brian Orakpo had left the team to go to the Tennessee Titans.
In his first two seasons, Culliver was usually used as San Francisco's third cornerback. He missed the 2013 season with a torn ACL in his left knee.
Last season, Culliver became a full-time starter for the 49ers, and he had four interceptions.
He drew unwanted attention for anti-gay remarks made during Super Bowl media day in 2013, and for an arrest in March 2014 on suspicion of felony hit-and-run and reckless driving.
Knighton, nicknamed "Pot Roast," is listed by the Redskins at 6-foot-3 and 331 pounds. He has played six seasons in the NFL, four with the Jacksonville Jaguars and two with the Broncos.
Known more for his prowess against the run than as a pass rusher, he has 12 ½ sacks in his career.
The Redskins went 4-12 last season, finishing in last place in the NFC East for the sixth time in seven years.