The woman was discovered lying by the side of the road near Trégonneau on the route between Guingamp and Tréguier in Brittany on Monday evening at around 10pm.
Passing motorists called emergency services but the 50-year-old British national was already dead, regional newspaper Ouest France reported.
Police have opened an investigation but have been unable to determine exactly how the woman died and how she ended up by the side of the road.
According to French news site France Bleu, the woman’s British partner has been arrested by police, although this has not been confirmed by authorities.
Commander Tourtin from the local gendarmerie told Ouest France that they were not ruling anything out at this stage.
An autopsy was carried out on Tuesday which determined that the woman died from a fractured skull. However, what caused the fractured skill, whether a passing car or a stone, is still not known.
There were also reports her body was covered with bruises.
Police have so far declined to name the woman but she is believed to have lived nearby with her British partner. Her body was found just a few metres from a farmhouse where her friends lived, Ouest France reported.
Officers were seen searching the local area and questioning neighbours and friends in the area.
A police investigator declined to comment to The Local on Wednesday, simply saying the investigation was ongoing.