Joseph Zadroga — a fierce advocate for first responders who suffered illness after the 9/11 attacks — died in a freak accident on Saturday when he was struck by an elderly driver who mistakenly hit the gas in a New Jersey parking lot, cops said.

Zadroga — the father of late 9/11 first responder James Zadroga — had just visited his wife at the hospital when he was struck in the parking lot by 82-year-old driver James McNeal at around 2 p.m., according to the Galloway Township Police Department.

Joseph Zadroga, 76, of Little Egg Harbor, has been credited with spearheading the Zadroga Act for 9/11 families which helped deliver much-needed funds to the families of first responders.

He standing beside his parked Hyundai Tucson when McNeal tried to park his 2021 Nissan SUV at about 2 p.m. and hit the gas instead of the brake.

Zadroga was struck by the McNeal’s SUV and pinned underneath. First responders performed “life-saving measures” and rushed him to AtlantiCare Regional Medical Center Mainland Division, where he died.

Zadroga’s son, James, was a veteran NYPD cop who died in 2006 of a respiratory illness he developed after responding to the 9/11 attacks in Lower Manhattan.

His death — at just 34 years old — was attributed to the presence of a variety of particles in his lungs.

The Zadroga family became famous after lending their name to a 2011 law that provided health benefits and compensation to others who fell ill after responding to the World Trade Center site.

After his son’s death, Joseph Zadroga and other activists pushed hard to extend the law for 25 years past its initial 2016 expiration date.

“I just want everybody out there, the victims who got sick, to have the health care that they deserve, because Jimmy didn’t get it,” Zadroga said at a 2014 rally near Ground Zero, and he wept when he remembered that his son could barely walk up the stairs in the end.

“Jimmy did not get the health care that he deserved, and I don’t want other families to go through what we did,” the long-suffering dad said.

The following year, the program was reauthorized until 2090, according to the CDC.

More than 86,000 first responders and nearly 41,000 other survivors who worked, lived or went to school in the declared disaster area have enrolled since its inception, the agency’s website said.

On Sunday, Zadroga’s legacy was remembered by those who joined his passionate fight.

“Joseph Zadroga was indispensable to the struggle to get 9/11 responders and survivors the help they needed and deserved from Washington,” Benjamin Chevat, executive director of Citizens for the Extension of the James Zadroga Act, told The Post.

“For years, he personally gave voice to his son James and the others still dealing with the impact of toxins from Ground Zero.”  

Galloway police are still investigating the accident, the department said.