The 55-year-old said he had a consensual relationship with Mounia Rabbouj, a French Muslim woman, who accused him of raping her nine times between 2013 and 2014, lawyer Emmanuel Marsigny said.
"The magistrates considered, following explanations from Mr Ramadan and some documents that he was able to provide, that there was no need to investigate Mr Ramadan concerning" the third woman, he added.
"He explained at length to the magistrates... that there had been sexual games, that there had been sexual relations as well, but that they were always freely consensual."
The prominent TV pundit and Oxford University professor, whose grandfather founded Egypt's Muslim Brotherhood movement, has been held since February on charges that he raped two women in France.
A third and fourth complainant later came forward.
Marsigny said the latest news marks a "turning point" in the case.
Many of Ramadan's supporters -- including two million Facebook followers -- insist Ramadan has been unfairly targeted because he is Muslim, while his lawyer has slammed what he describes as "lies" and inconsistencies by Ramadan's accusers.
A second woman, who is disabled, claims that Ramadan raped and beat her in a hotel in the southeastern city of Lyon in 2009.
Rabbouj, his third accuser, filed her complaint in March.
A fourth woman has filed rape charges in Geneva against Ramadan.
Judges last month refused bail for Ramadan, a Swiss citizen, who is being treated behind bars for multiple sclerosis.
He has denied wrongdoing and is suing.
(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)