The Ward family filed the lawsuit in Lewis County Supreme Court, which covers the Ward home in Port Leyden and is about 175 miles northeast of Watkins Glen International, where Stewart practiced Friday in preparation for the Sprint Cup Series race Sunday.
"Our son was truly the light of our lives and we miss him terribly every day," Ward's parents said in a statement. "Our hope is that this lawsuit will hold Tony Stewart responsible for killing our son and show him there are real consequences when someone recklessly takes another person's life."
A spokesman for Stewart said the driver had no comment.
Stewart was not criminally charged in the death of Ward, who had gotten out of his car and run toward Stewart's as Stewart drove under caution during the Empire Super Sprints race Aug. 9 at Canandaigua Motorsports Park. Ward was declared dead 45 minutes after being struck by Stewart's car, with the cause of death listed as massive blunt force trauma.
The lawsuit does not specify the amount of damages the family is seeking in claims of wrongful death, reckless conduct, gross negligence and Ward's suffering between the time he was struck and his death.
The lawsuit contends that Stewart gunned his 700-horsepower car as he drove by Ward, causing it to slide and strike Ward with the right rear tire, tossing him an estimated 25 feet.
"Stewart could have easily acted reasonably and with prudence to avoid striking Ward, just as all other drivers had done as they passed Ward during the yellow caution flag," the lawsuit states. "Stewart acted with disregard for Ward's life and safety by driving his vehicle in a manner that would terrorize Ward and thereafter strike, severely injure and kill Ward."
The case likely will hinge on whether the Ward family can prove that Stewart has some percentage of fault in Ward's death. If the case goes to a jury, its members would have to decide whether Stewart had a duty to drive in a certain manner under caution and whether he breached that duty.
"I just know in my heart that it was 100 percent an accident," Stewart said after the Ontario County (N.Y.) grand jury decision not to charge in him in September.
The grand jury watched two videos of Stewart's car striking Ward, and Ontario County District Attorney Michael Tantillo said they showed "no aberrational driving" by Stewart before his car hit Ward. Ward had marijuana in his system at the time of his death, Tantillo said when announcing the grand jury decision.
A three-time Sprint Cup champion, Stewart skipped the Watkins Glen race the day after the incident and missed two additional races. Stewart, who has not competed in a sprint-car event since that Canandaigua race, has had few highlights and no victories since then and sits 25th in the 2015 standings.
"I'm trying to not think about [the incident]. ... Unfortunately I have a feeling it is going to be brought up a lot this week," Stewart said Wednesday. "It doesn't help you continue to move forward with it."
The Ward family is represented by Mark Lanier of The Lanier Law Firm in New York.
"A jury needs to see the video, learn of Tony Stewart's past, and give the verdict that delivers justice," Lanier said. "Tony's actions took the life of a marvelous young, talented man."
Stewart is represented by notable Indianapolis attorney James Voyles, whose clients have included boxer Mike Tyson, former Indiana University men's basketball coach Bob Knight and Indianapolis Colts owner Jim Irsay.
New York law does not allow the Ward family to collect damages for their own pain and suffering but does allow parents to recover loss of expected future support and care that their child could have provided.
Tony Stewart being sued for wrongful death
ESPN NASCAR reporter Bob Pockrass reacts to the news that Tony Stewart is being sued for the wrongful death of Kevin Ward Jr. in an on-track incident last August.