McClellin (6-3, 245) started 31 games in four seasons with the Chicago Bears. He's played in multiple schemes and has lined up at defensive end, outside linebacker and inside linebacker.
"We feel like his arrow is still pointing up, especially at the inside linebacker position," Bears general manager Ryan Pace said at the combine.
In the Seahawks' scheme, McClellin most likely fits at strong-side linebacker, the spot vacated by Bruce Irvin. He hasn't put up big numbers as a pass rusher (7.5 sacks in 52 games) but set a career high with 81 tackles in 2015.
McClellin could take on Irvin's responsibilities in the Seahawks' base defense, and the team could decide whether or not to replace him in sub packages, depending on what other personnel they have available.
A first-round pick (19th overall) back in 2012, McClellin turns 27 in August.