"I'm not ashamed of my past anymore," Lanita Carter told CBS News. "I'm not ashamed of what naysayers say."
Carter, who was once Kelly's hairdresser, claims the R&B star tried to force her into oral sex in 2003. When she resisted, he allegedly masturbated and spat in her face.
Kelly has consistently denied all the charges against him.
Carter, who was 24 at the time of the alleged attack, said she had decided to speak out after watching Kelly's explosive TV interview with Gayle King, in which he tearfully claimed his accusers were "trying to kill" him.
"I felt like it should be a crime... that he be able to get on television and lie," Carter said.
"It's actually the reason I'm here."
With tears rolling down her face, the 40-year-old described how she had thought of Kelly as "a brother" and defended him against earlier allegations of abuse.
"I would tell people, 'pray for him'. He is nothing like they say," she told CBS News correspondent Jericka Duncan.
She went on to recount her alleged assault in graphic detail, and described the lasting impact it has had on her life.
"I've been carrying this since 2003," she said. "I have had to sit on a public bus and watch public conversation: 'Did you hear about what they did with R. Kelly? They need to leave that man alone.'
"And I can't stand up for myself."
Carter went to police on the day of the incident in February 2003; and later signed a $650,000 settlement with Kelly, in which the star denied wrongdoing.
Six years later, the singer released a song called Hair Braider, in which he described having sex with a hairdresser.
That led to another confidential settlement, this time for $100,000, in which Kelly agreed to stop performing the song. Again, he admitted no wrongdoing.
Carter is breaching both of these settlements by coming forward.
She said she was convinced to speak by Cook County State's Attorney Kimberly Foxx, who appealed for victims to contact her in the wake of the documentary series Surviving R Kelly.
Responding to Carter's interview, Kelly's lawyer said: "These allegations were fully investigated by the police and prosecutors and a decision was made after evaluating all of the evidence not to bring any charges".
Kelly is currently out on bail after being charged with 10 counts of aggravated criminal sexual abuse.
Three of his alleged victims were underage, while Carter was 24 at the time she says she was attacked.
The 52-year-old, who faces up to 70 years in prison if convicted, has pleaded not guilty to all of the charges.