the 76-year-old billionaire harassed massage therapists and forced one staff member to have sex with him. Mr Wynn has denied wrongdoing, calling the stories “preposterous”.
RNC chair Ronna McDaniel told US media she had accepted his resignation.
Mr Wynn has blamed his ex-wife, whom he is fighting in court, for the “slander”.
“The instigation of these accusations is the continued work of my ex-wife Elaine Wynn, with whom I am involved in a terrible and nasty lawsuit,” the billionaire said in a statement that his public relations team sent to the BBC on Friday.
What he is accused of
According to the Wall Street Journal, which said it had interviewed dozens of people who worked with Mr Wynn, he is accused of engaging in a pattern of abuse in which he often harassed massage therapists while alone in his private office.
The gambling industry giant paid $7.5m (£5.2m) to one manicurist who alleged she had been forced into sex by Mr Wynn, the paper claims citing court documents.
Female employees would fake appointments in order to avoid seeing him, or enlist others to pretend to be their assistants in order to avoid being alone with him.
Some would even hide in bathrooms or closets if they heard he was coming to their salon, the paper claimed.
Democrats attack Republican ‘silence’
Mr Wynn is also a Republican Party donor and fundraiser.
After harassment allegations were made against Hollywood executive producer Harvey Weinstein last year, Ms McDaniel and other leading Republicans called for the Democratic Party to return his donations.
Now some Democrats are asking if the same rules should apply regarding allegations against Mr Wynn.
The Democratic National Committee has attacked the RNC for remaining silent.
In an October statement, Ms McDaniel wrote: “If Democrats and the DNC truly stand up for women like they say they do, then returning this dirty money should be a no brainer.”