Ousted former Thai Prime Minister Yingluck Shinawatra arrives at the Supreme Court in Bangkok, Thailand, August 31, 2015. [Photo/Agencies]

She insists she acted honestly in administering the policy, which was widely criticised for distorting global prices and saw Thailand lose its crown as the world's top rice shipper.

Yingluck, 48, was greeted with applause and handed red roses by a crowd of supporters as she arrived at the court.

"I came to give moral support," said Sangiam Thongnak, 61. "She did the right thing."

Yingluck's supporters see the court case as another strike by a royalist establishment threatened by the rapid political rise of a clique of upstart capitalists from outside Thailand's traditional patronage network.

She won millions of votes by reviving the populist policies of her billionaire brother and former premier Thaksin Shinawatra, whom the Supreme Court jailed in absentia in 2008 for abuse of power, two years after he was ousted in a coup.

Prosecutors expect the Supreme Court proceedings to last at least six months. Some experts have said the junta risks a backlash if Yingluck's supporters perceive the verdict as unfair.