According to Adam Schefter (via this ESPN report), Avril's deal will be for two years and is worth $15 million.
The 26-year-old pass-rusher has played the last five NFL seasons with the Detroit Lions, recording 39.5 sacks and 16 forced fumbles. He started all but one of 32 regular-season games over the past two seasons, racking up over 20 sacks since the start of 2011.
Avril struggled down the final stretch of the 2012 season, recording just five combined tackles and failing to pick up a single sack over the Lions' last three games. Despite Detroit's eight-game losing streak to end the year, Avril still managed to lead the team with 9.5 sacks.
A native of Jacksonville, Fla., Avril is an athletic and durable end at 6'3", 260 pounds.
He burst onto the scene with Detroit in 2011, helping lead the Lions to a 10-6 record and a playoff berth that year. Avril finished second in the NFL with six forced fumbles and tied for 11th with 11 sacks in 2011.
Avril became an unrestricted free agent this offseason after the Lions placed the franchise tag on him a year ago.
Now he'll join an up-and-coming Seahawks team that is looking to make a serious push in 2013 and beyond.
Follow Bleacher Report Featured Columnist Patrick Clarke on Twitter.