Mr Paull rejects that he espouses that view, but has stood down nonetheless.
"David absolutely rejects the views he is quoted as supporting, but has stood down to not become a distraction from the important issues The Greens are focused on," a NSW Greens spokesman said.
"The Greens will take down all campaigning material in his name."
The candidate has admitted to The Australian that he made the post but only in an effort to investigate Port Arthur conspiracy theorists.
"I made those comments after an admin asked new members to justify their presence in the group. I absolutely do not believe, and have never believed, that Port Arthur was a conspiracy, nor do I have any doubt Martin Bryant was guilty of that horrendous crime," he told the paper.
Greens senator for Tasmania Nick McKim says he wasn't impressed with the Facebook commentary.
"I was appalled by those comments, they've got no place in our party. That's why the candidate has now stood down and I'm very pleased that he has," he told reporters in Hobart.
The party will review its processes for checking over candidates on the other side of the election, the senator added.
"I think you could mount an argument that every single political party could improve its vetting processes."