BANGKOK — When the Supreme Court of Thailand convicted former Prime Minister Yingluck Shinawatra of negligence and handed her a five-year prison sentence on Wednesday, she was nowhere near the courthouse in Bangkok.

Ms. Yingluck fled the country last month, when the verdict was originally supposed to be delivered, presumably fearing just such a jail term. It was the latest dramatic episode in a political crisis that has gripped Thailand for more than a decade, sending an Asian democracy sliding back to military rule.

In the Supreme Court’s verdict on Wednesday, Ms. Yingluck was found negligent in her supervision of a rice-subsidy program that delivered generous crop prices to Thailand’s large population of farmers. The program won her Pheu Thai Party votes, but Thailand’s current military government says it wasted billions of dollars, as stockpiles of unsold rice decayed in warehouses.

Supporters of Ms. Yingluck who had gathered outside the Supreme Court dismissed her two-year trial as politically motivated. The guilty verdict means that Ms. Yingluck will be banished from Thai politics for life. She could have been jailed for up to 10 years.