Dr Jeremy Richman, 49, was found dead at Edmonton Town Hall in Connecticut on Monday about 7am (local time), Newtown Police Department wrote on Facebook.
“The death appears to be a suicide, but police will not disclose the method or any other details of the death, only to state the death does not appear to be suspicious,” police said.
Dr Richman was the father of Avielle, 6, who was fatally shot alongside 19 other children aged between six and seven years old.
Her father started the Avielle Foundation in honour of his daughter.
The foundation aims at understanding and preventing violence through studying the human brain.
Dr Richman, a neuroscientist, spoke about the foundation at the Florida Atlantic University last week.
He said that on the morning of the shootings, he had planned to take Avielle to see the “Christmas Spectacular” show at Radio City Music Hall.
But she wanted to go to school to build a gingerbread house.
“I put her on the bus and said goodbye, expecting to just go back into the school a couple of hours from then,” Dr Richman said, according to Yahoo News US.
“She was one of the 20 kids murdered in the classrooms and six educators, and that changed everything.”
Newtown Police Department Lieutenant Aaron Bahamonde said Dr Richman’s death was “a heartbreaking event” for not only his family but the entire community.
“The police department’s prayers are with the Richman family right now and we ask that the family be given privacy in this most difficult time,” he said in a statement.
News of the father’s death led to an outpouring of grief on Facebook.
“How does a parent ever work through the daily anguish one feels over losing a child in this manner?” one woman wrote.
“Deeply saddened by this additional loss from this heinous tragedy.”
Dr Richman’s death follows the deaths of two teenage survivors of last year’s Marjory Stoneman Douglas High School shooting in the space of a week.
Sydney Aiello, 19, died from an apparent suicide on March 17.
Just days later, a second unnamed male student also died.