Ms Yingluck arrived at polling unit No 32 at 8.10am, where her name is number 174 on the list of eligible voters.
A large number of police and soldiers were deployed at the school to provide security for the caretaker premier.
Her residence in Soi Yothin Pattana 3 was also heavily guarded.
After casting her vote, the prime minister urged all eligible voters to exercise their right to do the same.
She and other cabinet members are expected to monitor the rest of election day at the Office of the Defence Permanent Secretary at Muang Thong Thani on Chaeng Wattana Road.
Former prime minister Thaksin Shinawatra's ex-wife Potjaman na Pombejra and his daughters Pinthongta and Paethongtan also cast their votes on Sunday morning.