The man, Clinton Danner, was arrested Sunday at a Chicago hotel. He faces a felony charge and is being held on $150,000 bond. It isn't clear if he has an attorney.
"In this situation, we have a husband whose prostituting his wife out around the country while holding their 3-year-old child, threatening the wife that, if she doesn't go forward with this, he will take the child away from her and harm her," Dart said.
Prosecutors say Danner had been forcing his wife to do have sex with strangers since she became pregnant four years ago. She reportedly called a sex trafficking hotline for help, and that led to Danner's arrest.
Dart says he plans to notify Craigslist of the arrest, but he predicts the online classified site won't respond.
Last year, Dart filed a lawsuit alleging Craigslist had become the "largest source of prostitution in America." A judge dismissed the lawsuit.
(The Associated Press contributed to this report.)