Captured in Syria by a US-backed force fighting the ISIL, they are the first French ISIL members to receive death sentences in Iraq, where they were transferred for trial.
Named as Kevin Gonot, Leonard Lopez and Salim Machou, they have 30 days to appeal.
“They were sentenced to execution after it was proven that they were members of the terrorist Islamic State organisation,” said one court official, who declined to be named as he was not authorised to speak to the media.
Iraq has taken custody of thousands of ISIL fighters who were repatriated in recent months from neighbouring Syria, where they were caught by the US-backed Syrian Democratic Forces during the battle to destroy the ISIL “caliphate”.
Iraqi courts have placed on trial hundreds of foreigners, condemning many to life in prison and others to death, although no foreign ISIL members have yet been executed.