Orakpo tore his right pectoral muscle in the team's 19-17 victory over the Tennessee Titans on Sunday and is done for the season. With him out, Washington signed Brown for help at outside linebacker.
Brown signed with Washington during training camp and spent the entire preseason with them. He was released in the final round of roster cuts at the end of August.
Brown has also spent time with the Panthers, Chargers, Lions, Eagles and Cowboys. A former second-round draft pick in 2009, the linebacker had 10 tackles, one sack and one forced fumble in seven games with the Cowboys last season.
Orakpo will become an unrestricted free agent following the season after being given the franchise tag over the offseason. A three-time Pro Bowl selection, Orakpo is making $11.45 million under the tag.
Washington snapped a four-game losing streak with the win over the Titans. The team is 2-5 heading into Monday's game versus Dallas.
- Molly Geary