Compatriot Putharet Khongrak finished third in the event to secure Thailand's fourth bronze at the Games.
Defending champion Prawat, 40, had won the gold at four Paralympics -- in 2000, 2004, 2008 and 2016 -- while he got the silver medal in the 2012 Paralympics.
Putharet Khongrak, 26, had competed in the Paralympics for the first time. Putharet had also earned the bronze medal on Saturday in the men’s 5,000 metres T54 wheelchair race.
Meanwhile, the gold medal was won by Switzerland’s Marcel Hug, the runner-up from the previous Paralympics. He also won the gold medal in the men’s 5,000 metres T54 wheelchair race.
Prawat and Putharet will compete in one more race, the men’s 800 metres T54 wheelchair race. The qualification round will begin on Thursday.
With a gold, two silver, and four bronze, Thailand is 42nd on the medals table.