Stephane Sebag, a lawyer for the prisoner, whose name was not released, said the judge ordered his client released after visiting the cell herself to question the man, Radio France Internationale reported Thursday.
Sebag said the judge agreed the cell at the Bois-d'Arcy jail facility was too cramped to be shared by the two men, their beds, a table and a single chairs.
"To see a big lad like him, 1.94 meters tall (6 feet, 4 inches), who can't even get up and accomplish day-to-day tasks, it's unacceptable," Sebag said. "Between the two beds there's a space measuring 50 centimeters squared (7.75 square inches), and two people can't be in it at the same time. For eating, they have a single table and chair, and a little electric stove they made themselves."
Sebag said a hole in the ceiling above his client's bed let the weather into the cell.
"So, he has the choice of either getting his face wet as he sleeps, or his feet," he said.
Sebag praised the judge's decision as "courageous" and "extremely rare."
Prosecutors are appealing the man's release.
Authorities did not say for what the man had been imprisoned or how much time was left on his sentence.