The French Muslim woman, who wants to remain anonymous and uses the pseudonym "Marie", claims to have suffered multiple rapes in France, Brussels and London between 2013 and 2014.
She has accused Ramadan, 55, of subjecting her to violent and sexually degrading acts during a dozen meetings, often in hotels on the sidelines of conferences.
"I had to obey him, be available 24 hours a day, do whatever he told me, take pictures in submissive positions, on my knees to ask for forgiveness, call him 'master'," she told Europe 1 radio.
Swiss Islamic scholar Tariq Ramadan held in Paris on rape charges
"At first, there were feelings, otherwise I would not have agreed to see him," she added.
"I had difficulty saying the word: rape. Today I can say it."
A judicial source said: "'Marie' tried in vain to escape the influence of Mr Ramadan who did not stop threatening her," during a period between February 2013 and June 2014.
Ramadan, a prominent TV pundit and Oxford University professor whose grandfather founded Egypt's Muslim Brotherhood movement, was detained on February 2 over charges he raped two Muslim women in France, which he denies.
His two accusers went to police in late October, both alleging that he had raped them in French hotel rooms.
Henda Ayari, 41, said she decided to accuse him publicly after the "Me Too" campaign against sexual abuse and harassment encouraged her to speak out.
Ayari, a feminist activist who previously practised a conservative strain of Islam, says Ramadan raped her in a Paris hotel room in 2012.
The second accuser, a disabled woman, alleges that Ramadan raped her and beat her in a hotel in the southeastern city of Lyon in 2009.
Islamic scholar Tariq Ramadan to face French judge in rape, assault case
"Bringing forward a complaint can be a slow process. There will be others," said lawyer Eric Morain, who represents the second accuser.
Ramadan remains in custody as French authorities judge him a flight risk.
A court dismissed a bid by Ramadan last month to be released on health grounds, after his lawyers argued his multiple sclerosis and nerve damage could not be adequately treated behind bars.
His lawyers have also unsuccessfully attempted to secure his release by proposing handing in his Swiss passport, posting a bail of $62,000 and daily check-ins at a police station.
A professor of contemporary Islamic studies at Oxford, Ramadan has been on leave since November after the allegations emerged.
One of European Islam's best known figures, he has dismissed the accusations against him as a smear campaign by his enemies and his lawyers argue there are inconsistencies in the women's accounts.
His supporters — including two million Facebook followers — have lashed out angrily at his arrest, with many complaining that he has been unfairly targeted because he is Muslim.
COMMENTS
Comments are moderated and generally will be posted if they are on-topic and not abusive.
For more information, please see our Comments FAQ