The suspects were flown to France on 13 November, the day of the Paris attacks.
The two men, one from Lyon and the other from the southern port of Marseille, did not know each other before meeting up in Tunisia, a judicial source said.
The 20-year-old girlfriend of one of the men, a convert to Islam who authorities said had at one stage intended to join her partner in Libya, has also been charged with terrorist offences.
The Libyan city of Sirte is the first to fall to IS outside Iraq and Syria with the armed Islamist group profiting from the chaos that has followed the fall of Moamer Kadhafi.
Libya is “incontestably” the major challenge for the next few months, French Prime Minister Manuel Valls said on Tuesday.
The West’s “responsibility was to have not followed up on the intervention” that toppled Kadhafi, he told Europe 1 radio.
Source: rfi afrique