The men's bodies were found by emergency services yeterday night in a black vehicle with no number plates.
The men were 22 and 20 years old. While one had been known to police for drug use, the other had no criminal record.
A third, lightly wounded man aged 24 was also found in the car. He was taken into custody, the Marseille prosecutor's office said.
The men had been attacked by "two men on a scooter. One was armed with a Kalashnikov-style rifle, the other with a handgun," prosecutor Xavier Tarabeux said.
Most of them have been gangland killings.