Kamol Duangpasuk, known among the red shirts as Mainueng Kor Kuntee, was gunned down in the parking lot of Krok Mai Thai Lao restaurant on Lat Pla Khao Soi 24 at 2.10pm.
Witnesses said they heard 5-6 gunshots after Mr Kamol left the dining area. They rushed out and found him in the parking lot.
He died at Mayo Hospital.
Kamol, a native of Samut Songkhram's Amphawa district, graduated from Silpakorn University.
He wrote poems for Matichon Weekly for several years, as well as several books.