Shinawatra faces impeachment by the National Legislative Assembly (NLA) over the controversial rice-subsidy programme, which, though popular, cost billions of dollars and triggered protests that toppled her government.
She also faces charges of dereliction of duty in supervising the programme.
Yingluck, who showed up at parliament this morning amid tight security, has said she is ready to defend all the charges against her.
Carrying 30 documents containing 139 pages to clarify her position, a smiling Yingluck was greeted by her supporters outside the parliament. But no huge crowd arrived as was anticipated.
"I ran the government with honesty and in accordance with all laws," she told the assembly.
"The rice pledging scheme... (was) aimed to address the livelihood of rice farmers, their debts and falling rice prices," said Yingluck in an impassioned defence before the assembly.
The lawmakers are likely to vote on their verdict by the end of the month. If impeached, Yingluck could be banned from politics for five years.
According to analysts, the impeachment is more about the attempt to keep the powerful Shinawatra family, whose parties have won every election since 2001, out of politics.
Yingluck's supporters also say the proceedings are part of a wider campaign to end the influence of Shinawatra clan.
The NLA began the proceedings prosecuting a motion filed by the National Anti-Corruption Commission against Yingluck for alleged dereliction of duty in supervising the rice- pledging programme.
Yingluck has insisted that Thailand's fragile democracy was under attack from protesters and the army, which staged a coup on May 22 that threw her administration out.
Yingluck's brother, Thaksin Shinawatra, was also ousted by the army in a 2006 coup.
The closing statements will be made on January 21 and the NLA, hand-picked by the junta and dominated by active and retired military officers, will hold a meeting to vote in the next three days.

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