Kwanchai Praipana, who leads thousands of red-shirted pro-government supporters in Udon Thani province, was sitting outside his home when he was shot by unidentified assailants, police said. He was wounded in the arm and leg.
"From what we saw on CCTV, a bronze pickup truck drove by and several rounds were fired at the house," Police Colonel Kowit Tharoenwattanasuk told Reuters.
"The investigation has just begun but we believe this is a politically motivated crime."
The shooting could further raise tension in the country after Prime Minister Yingluck Shinawatra's government imposed a state of emergency in the capital, Bangkok, from Wednesday to help contain a protest movement trying to force her from power.