The suit, filed in California Superior Court, blames the NFL for its "acts or omissions" that hid the dangers of repetitive blows to the head.
chronic traumatic encephalopathy (CTE).
"Our attorneys will review it and respond to the claims appropriately through the court," NFL spokesman Brian McCarthy said in a statement.
The family is also suing Riddell, Inc., the manufacturer of NFL helmets, for its "negligent" design.
Seau spent 13 seasons with the Chargers, helping the franchise to their only Super Bowl appearance after the 1994 season. He also played three years for Miami and four more for New England before retiring after the 2009 campaign.