Prosecutors seized documents from the office and Jean Gachassin's house.
The investigation relates to alleged corruption over ticket sales for the French Open and a deal to extend the Roland Garros stadium where it is held.
The FFT confirmed its headquarters had been searched and said it was fully co-operating with investigators.
France's financial prosecutors office said in a statement it was investigating "misappropriation of property and influence trafficking", "an illicit system of reselling tickets for the French Open tournament", and the "awarding of the contract for the renovation and enlargement of Roland Garros".
A travel agency in Tarbes, southern France was also searched as part of the investigation, according to reports.
The world of tennis was rocked earlier this year after a joint BBC and Buzzfeed investigation revealed suspected widespread match fixing in professional tennis.
The French Open starts on 22 May.
The headquarters of the French tennis federation (FFT) and the home of its president have been searched following allegations of illegal ticket sales.