Bangladesh Samyabadi Andolon leader Jahed Ahmed Tutul was found dead in Sapmara area of Matiranga in Khagrachhari on Sunday.
Police recovered his motorcycle and a bag from the spot.
His body was spotted under a bridge on the Khagrachahri-Chittagong Road in Sapmara area.
Matiranga police Officer-in-Charge (OC) Muhammad Ali said it could be a road accident.
"An autopsy will be performed at Khagrachhari Sadar Hospital to know the reason behind his death," he said.
Tutul's colleague Rafiqul Islam said: “Tutul dropped off one of their colleagues Dr Sushanto Barua in Zero Mile area of Khagrachhari at 8pm on Saturday and set off for Matiranga.”
As Tutul did not return to his home at night, his colleagues started looking for him in the morning. At one point, they found his body under the bridge in Sapmara and informed the police, Rafiqul Islam said.
Tutul, 60, was the convener of the party's Khagrachhari district unit.
Professionally a farmer, Tutul was a resident of Babupara area in Matiranga.