Yingluck, the kingdom's first female premier and the sister of former leader Thaksin Shinawatra, was toppled from office by a controversial court ruling shortly before the army staged a coup in May.
She faces impeachment tomorrow by the junta-picked National Legislative Assembly over her administration's populist rice subsidy programme, which funnelled cash to her rural base but cost billions of dollars and inspired protests that felled her government.
"There is no position to remove me from as the Constitutional Court has already removed me as prime minister," she told assembly members, also saying she should not be impeached for violating a constitution that no longer exists under junta rule.
Yingluck also defended the rice scheme as an attempt to support Thailand's rural poor, who historically receive a disproportionately small slice of government cash.
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"I am not corrupt, I was never careless," she said, urging members to consider her case with fairness and "without being guided by anyone".
A guilty verdict would bring an automatic five-year ban from politics and risks enraging her family's 'Red Shirt' supporters, who have laid low since the coup.
Speaking before the hearing Thursday, Jatuporn Prompan, chairman of the Red Shirts, cautioned against street protests on his television show, after noting signs he believed would "lead to impeachment".