"We were at the Venice Film Festival and he tried to rape her," Perkins said of the alleged incident involving a then-colleague.
The colleague was shaking and in shock and also did not want anyone to find out about the matter, said Perkins, who said she then called Weinstein out of a business meeting to confront him.
He denied the accusation.
"He said nothing at all had happened and he swore on the life of his wife and his children, which was his best get-out-of-jail card that he used quite a lot."
Both Perkins and the colleague subsequently resigned and, Perkins said, she expected criminal proceedings to follow, but her legal team made it clear the options were limited.
"The lawyers made it very clear that we did not have many options. Because we hadn't gone to the police when we were in Venice, we had no physical evidence and ultimately it would be two under-25-year-old womens' word against Harvey Weinstein, Miramax Film Corporation and, essentially, the Disney company."
Speaking about working for Weinstein in her early 20s, Perkins spoke about the cult of personality surrounding him in his heyday.
"Harvey, now, everyone sees as this sort of repulsive monster, which he was and is on one hand, but I think what is interesting and what isn't maybe brought forward is that he was also an extremely exciting, brilliant, stimulating person to be around," she said.
Weinstein's lawyers repeated the denial of all allegations of non-consensual sex in a statement given to Newsnight. Reporter Emily Maitlis said Disney had not yet responded to a request for comment and Miramax had declined to comment.
It comes amid revelations from movie directors that Weinstein attempted to blacklist actors Mira Sorvino and Ashley Judd from Hollywood in a smear campaign which cost both actors roles in major films.
Lord of the Rings director Peter Jackson told New Zealand's Stuff that Weinstein and his brother Bob are a pair of "second-rate Mafia bullies" who talked him out of casting Sorvino and Judd in the Lord of the Rings series in the late 1990s.
Both women are among the growing number who have accused Weinstein of sexual harassment.
Meanwhile, weeks before the Weinstein sex scandal broke, the now-disgraced mogul approached Netflix in a $25 million bid to save his own skin.
Aware that both the New York Times and Ronan Farrow were working on stories detailing his alleged sexual harassment and abuse of actors and female employees, Weinstein approached Netflix, seeking "emergency cash" — in hindsight, possibly "hush money" to save his own skin — but without revealing the exact reason for his need of a financial lifeline. Other Hollywood insiders said Weinstein was looking to sell the rights to part of his movie catalogue in exchange for around $25 million.
When asked about his Netflix request, reps for Weinstein said, "Untrue. Nonsense." Netflix — which has downplayed its relationship with Weinstein — declined to comment.
