SPT won 15 out of 269 seats in the 1975 parliamentary elections.
Punyodyana was murdered on February 28, 1976. Around 10,000 people participated in his memorial.
After the Thammasat University massacre on October 6, 1976, many SPT cadres went into exile or joined the Communist Party of Thailand's guerrillas in the border areas with Laos in Northern Thailand and Isan (Northeastern Thailand). Thus the party was dissolved.