The Waratahs full-back, 30, was sacked in April but requested a hearing, which was heard by a three-person panel.
They found him guilty of a “high level breach” of RA’s player code of conduct and have upheld the dismissal.
Folau, who has won 73 caps and was contracted with RA until 2022, has 72 hours to appeal against the decision.
An appeal would mean a second code of conduct hearing with the same evidence but a new panel, while he could also try to take his case to Australia’s Supreme Court.
The fundamentalist Christian posted a banner on his Instagram account in April that read: “Drunks, homosexuals, adulterers, liars, fornicators, thieves, atheists and idolators – Hell awaits you.”
Folau escaped punishment for similar comments last year.
“This outcome is a painful situation for the game,” said RA chief executive Raelene Castle.
“Rugby Australia did not choose to be in the situation, but Rugby Australia’s position remains that Israel, through his actions, left us with no choice but to pursue the course of action resulting in today’s outcome.”
Folau was expected to play at this year’s World Cup in Japan but Wallabies coach Michael Cheika has said he is unlikely to be selected for Australia again.
“This has been an extremely challenging period for Rugby,” added Castle.
“This issue has created an unwanted distraction in an important year for the sport and for the Wallabies team.
“But our clear message for all Rugby fans is that we need to stand by our values and the qualities of inclusion, passion, integrity, discipline, respect and teamwork.”
He has recently lost sponsorship deals with Land Rover, who withdrew a car issued to him, and sportswear brand Asics.
“There have been many opportunities to potentially make the situation a little bit easier,” said Folau, when speaking to his church congregation in Sydney on Sunday.
“I could go back and play the game, get everything back to the way it used to be.
“The way Satan works is he offers you stuff that could look good to the eye and makes you feel comfortable, and if you go down that path all the worries and troubles will go away.
“It is always the will of God that comes first.”