Former Lieutenant Governor Lise Thibault has to report to jail.
Quebec's Court of Appeal has rejected Thibault's attempt to overturn her 18-month sentence for fraud and breach of trust.
In 2014, Thibault pleaded guilty to claiming more than $700,000 in improper expenses while she was the Queen's representative in Quebec.
Thibault was sentenced in September 2015 and spent six nights in custody before launching her appeal.
Lawyer Marc Labelle had argued Thibault deserved a lesser sentence because of her age and disability. Thibault is 76 years old, needs a wheelchair to get around, and has anxiety attacks.
When Thibault was sentenced, Judge Carol St-Cyr said her behaviour was "highly reprehensible."
