Seau's children and ex-wife, along with the trustee of his estate, also claim in the San Diego Superior Court lawsuit that the NFL has long concealed from its players and the public the risks of neurological injury in the sport.
"We know this lawsuit will not bring back Junior," the Seau family said in a statement. "But it will send a message that the NFL needs to care for its former players, acknowledge its decades of deception on the issue of head injuries and player safety, and make the game safer for future generations."
An NFL spokesman, Greg Aiello, told Reuters in an email that the league's attorneys would review the lawsuit and respond to the claims appropriately in court.
Seau, a 12-time Pro Bowl linebacker for the Chargers and two other NFL teams during his two-decade career, died last May after shooting himself in the chest at his beachfront home in Oceanside, California.
The lawsuit filed by his family, which claims fraud, negligence and wrongful death, seeks unspecified damages from the league and several football helmet makers.
It comes seven months after some 2,000 ex-NFL players sued the league in federal court in Philadelphia over similar allegations, consolidating more than 80 lawsuits.
A study by independent researchers found that Seau, 43, suffered from chronic traumatic encephalopathy, or CTE - the same debilitating brain disease diagnosed in at least two other former NFL players who committed suicide.
The NFL has said the findings about Seau's brain underscored "the recognized need for additional research to accelerate a fuller understanding of CTE." League teams have donated $30 million to the National Institutes of Health for research.
Concerns over the risk of brain injury from repeated concussions suffered by players in the NFL are growing. Football is America's most popular television sport and a $9 billion a year industry.
The league has attempted to institute rule changes protecting player safety while still preserving the spectacle fans enjoy, which is partly based on the speed and power of colliding athletes.
The Seau family says in their lawsuit that the NFL has long known that head trauma suffered by professional football players carried the risk of brain injury, while at the same time marketing the ferocity and brutality of the game.
"Instead of being honest about the dangers and working with both players and the medical community to minimize them, the league repeatedly asserted that professional football players were at no greater risk of brain or neurological injury than the public at large," the family says.
The complaint also details in grim terms Seau's battle with what the family believes were symptoms of CTE, including dizziness, depression, anxiety and insomnia.
"His increasing emotional instability resulted in uncharacteristically self-destructive, aggressive and violent behaviour," the lawsuit says, adding that he became a compulsive, manic gambler and lost significant amounts of money.
Seau shot himself just weeks after former Atlanta Falcons safety Ray Easterling committed suicide at age 62. Easterling's family described a long descent into dementia following his retirement from the NFL, and an autopsy revealed indications of CTE.
In February 2011, four-time Pro Bowl safety Dave Duerson, who played most of his career with the Chicago Bears, shot himself in the chest. In a suicide note, he donated his brain for study, and it was found to exhibit signs of CTE.
CTE, once known as boxer's dementia, is caused by repeated impacts to the brain, and has been found in athletes who suffered head injuries as well as in members of the armed forces with concussive injuries from blast waves.
Because the mild and moderate brain injuries do not show up on CT scans or other imaging, the condition can be definitively diagnosed only through an autopsy.
