The trial of Strauss-Kahn, who saw his stellar career plummet to earth after a separate sex scandal that resulted in his arrest in New York in 2011, opened in the northern French city of Lille a week ago.
He has denied aiding and supporting the prostitution of seven women.
Asked by the judge Tuesday if his position had changed, Strauss-Kahn said he knew nothing of the "prostitutional nature" of the parties in which he took part.
He also faced questions over claims by one of the sex workers that he had brutal sexual relations with her and must have known she was being paid. Other defendants insist Strauss-Kahn wasn't told.
In France, prostitution is legal, but pimping is not.
The trial is being closely watched both in his homeland, where Strauss-Kahn is commonly known as DSK, and around the world.
There were dramatic scenes as Strauss-Kahn's car arrived at court Tuesday, when topless protesters with anti-DSK slogans painted on their bodies clambered onto his car. The activists, from the feminist group Femen, were then bundled away by police.
Former sex worker: 'We were there for him'
Prosecutors say the operations of the prostitution ring, organized from the Hotel Carlton in Lille, stretched all the way to New York and Washington. Sex workers involved in the parties said they were like orgies.
Strauss-Kahn, who was married to French TV journalist Anne Sinclair until their divorce in 2013, has never denied that he took part in the parties. But the crux of his defense is that he did not know prostitutes were involved.
If the court finds Strauss-Kahn guilty of the charges, the former IMF director could be sentenced up to 10 years in prison and fined 1.5 million euros ($1.7 million.)
A former sex worker who's one of the plaintiffs in the case, named only as Mounia R., described an encounter with Strauss-Kahn at the Murano Hotel in Paris when she took the stand Tuesday.
She told the court she had indicated that she didn't like the sexual practices in which they were engaging and that Strauss-Kahn registered this. He remained smiling when she cried, she said. However, she said, she consented to the brutal sexual act because she needed the money.
The woman also said that her presence at the hotel was "essentially for DSK," adding, "I was told we were there for him."
The former sex worker contended that none of the participants in the parties could have been unaware that the women involved were prostitutes.
Questioned by the judge, Strauss-Kahn denied having seen Mounia R. crying while they were having sex, and he said he would have been petrified if he had noticed.
He also said he'd been given no sense of refusal by her. Referring to other testimonies in the case, he said other women had refused to have sex with him at the parties and that he'd accepted their decision. "When others said no, it was no," he said.
Asked why fellow defendant Fabrice Paszkowski, a friend and businessman, would not have told him the women were being paid for sex, Strauss-Kahn said Paszkowski knew he did not like prostitution.
His friend wanted to please him by telling him the women were just "libertines," Strauss-Kahn said, and didn't realize the risk this represented for him.
As to Mounia R.'s claim that he must have been aware she was a sex worker, Strauss-Kahn said that she had provided no concrete evidence to demonstrate that he knew.
Another defendant in the case, businessman David Roquet, denied having told Mounia R. that she was essentially there for Strauss-Kahn, also a friend of his.
Prosecutors say Roquet and Paszkowski picked up the bills for the sex parties for their influential friend.
Another defendant, Beatrice Legrain, an occasional sex worker who's also accused of being a pimp, also testified Tuesday.
Paszkowski said she was introduced to Strauss-Kahn as a restaurant owner and the prostitute she accompanied to a party as a restaurant employee.
Paszkowski reiterated that the former IMF director was not supposed to know the status of the women.
The judge asked Paszkowski and Jean-Christophe Lagarde, a former senior policeman also accused in the case, if they were expecting professional benefits from their friendship with Strauss-Kahn, whom many people once saw as a future president of France. They denied that was the case.
Paszkowski and other defendants have previously been adamant that Strauss-Kahn was unaware the women were prostitutes and that he never paid them.
The prosecutor's office in late 2013 asked for Strauss-Kahn's case to be dismissed, citing lack of evidence. However, the investigating magistrates did not follow their recommendations.
Altogether, there are 13 defendants in the case besides Strauss-Kahn, said Patricia Corbellego from Action Teams Against Pimping, one of the plaintiffs in the case.
'He has suffered a lot'
A biographer of Strauss-Kahn, Michel Taubman, told CNN that he believes the former IMF chief's story in what is known in France as the "Carlton affair."
"If he knew that the girls were prostitutes, I think he would not have made them come to Washington and he would not have had a picture of one of them in his office," said Taubman.
In the years since his New York arrest, Strauss Kahn has spent much of his time trying to clear his name. He has tried to revive his reputation and start a new career by creating an economic consultancy, taking on both private and governmental clients. He needs these clients, according to Taubman, in order to pay his legal bills.
Taubman says he does not believe Strauss Kahn can or will ever be directly involved in politics or policy making again.
"He is a father, a grandfather, he has suffered a lot, his family has suffered a lot. And I don't think he will have the energy or the will to come back in politics, you know," the biographer said.
Strauss-Kahn said almost as much himself in an interview with CNN's Richard Quest, long before the trial opened in Lille.
"So I made this mistake to believe that you could have a public life doing what you had to do in the public life. ... And that you can have a private life," he said.
"And my mistake was certainly to believe that you can have these two things together without any connection between. It was wrong. It was wrong in the way you say because people are not expecting this kind of heterodox behavior from somebody having public responsibility."
Presidential hopes dashed
The May 2011 sex scandal not only ended Strauss-Kahn's tenure as IMF director -- a role that gave him huge influence on the economies of countries around the world -- but dashed his presidential hopes.
He was the leading prospective Socialist candidate in the French presidential elections of 2012, an election his party won. Strauss-Kahn could well have taken the presidency, which instead was claimed by Francois Hollande
The scandal erupted when Strauss-Kahn was arrested at New York's Kennedy Airport on charges he had sexually assaulted a maid, Nafissatou Diallo, at a hotel where he had stayed. He resigned in disgrace from the IMF, and months of legal battles followed.
In the end, he was cleared of the charge
and allowed to return to France, only to find that his name had come up in connection with the alleged Lille prostitution ring.