The Dolphins are signing former Seahawks and Redskins linebacker Terence Garvin, a source tells Ian Rapoport of NFL.com (on Twitter). Garvin started in three games last year, but he has made his name as a special teams standout. 
Garvin, 28, entered the league as an undrafted free agent out of West Virginia in 2013 and spent the first three years of his career with the Steelers. He then went on to play for the Redskins in 2016 and the Seahawks in 2017.
Last year, Garvin saw the most defensive playtime (18%) of his career in 2017 due to injuries. All in all, he tallied nine tackles, one sack, and one forced fumble in 15 games for Seattle.
Garvin will serve as a reserve for the Dolphins while their search for a third starting linebacker continues.