The two consumed liquor at a bar in Mamallapuram and were returning to the city in a car when they halted on the highway to relieve themselves last night.
The client then suddenly took out a pistol and shot at the lawyer, Kamesh, in the hip, a police official investigating the case told PTI.
Kamesh immediately telephoned one of his friends, who rushed him to a private hospital in the city where doctors declared him brought dead, he said.