Armstrong has appeared in 39 career games and has 54 career receptions for 986 yards and five touchdowns.
Armstrong, 29, went undrafted in the 2005 NFL Draft and played in arena and indoor football before joining the Dolphins prior to the 2008 season. After time on the Dolphins practice squad, the 5'11, 179-pound receiver was released before he stuck with the Redskins.
In two seasons with the Redskins, Armstrong played in 29 games, making 13 starts, and accumulated 51 receptions for 974 yards receiving and five touchdowns. After he was released by the Redskins, he had a second stint with the Dolphins for the 2012 season and appeared in five games, but caught only three passes for 12 yards.
He has some experience on special teams, but has only returned one kickoff in his career. The Jaguars had a roster spot to fill and now have 53 players on their roster. Armstrong will wear jersey No. 13.