She faces impeachment over the loss-making rice subsidy programme which cost billions of dollars and was a driving force behind protests against her now toppled government.
Impeachment by the junta-appointed National Legislative Assembly carries an automatic five-year ban from politics, but could also galvanise her family's 'Red Shirt' supporters to protest after months of silence under martial law.
"We are confident it (the vote) will be done before the end of the month -- roughly the 22nd or 23rd," NLA deputy speaker Surachai Liengboonlertchai told AFP.
The hearing is scheduled to start around 10:00am.
A successful impeachment needs three-fifths of the 250-strong national legislature to vote in favour.
Prosecutors are also in the process of deciding whether Yingluck should face a separate criminal case over the rice subsidy scheme.
AFP