Thibault was facing eight counts for fraud, forgery and breach of trust in connection with allegations she misspent public funds.
She is pleading guilty to fraud and breach of trust, but not forgery, and is offering to pay back several hundred thousand dollars.
Thibault was first charged in 2009 after the Journal de Quebec revealed she spent public funds on herself and her family during her 10-year tenure.
Allegations of misspending first came to light at the end of her term, after a Quebec auditor's report challenged $711,200 of expenses, including housing and meals already paid for by the province.
However, the criminal case only alleged $291,000 in illegal spending.
Her trial had been adjourned in August after she began testifying in her own defence, because she had fallen ill.