Atogwe signed the deal Thursday, two weeks after he was cut following six seasons with the St. Louis Rams.
Kareem Moore started 11 games at free safety for the Redskins last season but was inconsistent and finished the season on injured reserve. He is recovering from right knee surgery.
The signing reunites Atogwe with Redskins defensive coordinator Jim Haslett. Atogwe spent three of his seasons in St. Louis playing for Haslett, who was the Rams' defensive coordinator and later interim head coach.
Atogwe has 22 career interceptions, including three last season.