The conditions at the prison in New Caledonia have been deemed unacceptable by members of the mission sent by the French Minister of Justice Christiane Taubira.
The prison, Camp Est, has recently been the scene of two attempted mutinies, and poor sanitation and overcrowding have been criticized for many years by human rights organisations.
Last year, Paris announced plans to extend the jail by 2016 but the city of Noumea has refused to issue a building permit.
AFP reports that led by a State Councilor, Mireille Imbert-Quaretta, the mission stayed a week, and met with nearly a hundred people, including inmates.
Ms Imbert-Quaretta told reporters conditions are absolutely unacceptable.
She says there are six inmates in cells of 11 square meters, and whoever is in the top bunk has only 50 inches above their head and can not not even sit down.
The mission is due to report to the minister on November 15.