A preliminary investigation into Thomas Fabius's financial affairs was opened in France in 2013, with police particularly interested in his purchase of a seven million euro (USD 7.6 million) Paris apartment.
A police source said the apartment, which was searched Tuesday, had raised alarms over money laundering.
Thomas Fabius's lawyer confirmed he was in custody but would not comment further.
The 34-year-old son of France's top diplomat is wanted in the United States for allegedly writing bouncing cheques at a Las Vegas casino.
His father, a former Socialist prime minister, was appointed France's foreign minister in May 2012.
Often photographed at high-flying parties, Thomas has spent millions of dollars in casinos in the past.
His high-profile father received a standing ovation in France's National Assembly today for his efforts in negotiating a historic climate deal in Paris agreed by 195 countries.
