"A trustworthy press is the immune system of democracy," Newmark said in a statement.
"As citizens, we can only make informed decisions when we have news we can trust. Independent investigative reporting is essential to shoot down false claims and expose bad actors. ProPublica is a leader in that kind of journalism, and we need more of it."
Newmark has a history of support independent news organisations. In 2016, the entrepreneur donated $1 million to the Poynter Institute, a non-profit journalism school. He additionally gifted $1 million to Wikipedia in 2016 to support its editorial and fact-checking efforts.