The Quebec government announced Wednesday it has asked provincial investigators to look into Thibault's spending when she was lieutenant-governor.
Federal Transport Minister Lawrence Cannon told Parliament several hours later that Ottawa would ask the RCMP to do the same.
Both the federal and Quebec auditors general issued reports Tuesday saying Thibault spent more than $700,000 over 10 years on events not linked to her official activities.
"In light of the facts alleged by the auditors general, I have asked the head of the Surete (QPP) to proceed as soon as possible with an investigation that he considers appropriate in the circumstances," Intergovernmental Affairs Minister Benoit Pelletier told the legislature.
Police will determine whether their report should be sent to Crown prosecutors, who would in turn decide whether to lay charges.
Thibault has emphatically denied any wrongdoing.
"In my 10 years on the job, I always acted in good faith," she said Tuesday.
"Those who know me know I am an honest person."
Thibault, who uses a wheelchair, defended some of the transport and security costs incurred on her watch, saying there was no way to get around her physical condition.
She is expected to meet with government representatives shortly to discuss the possibility of repaying all or part of the money.
Pelletier told a legislature committee Wednesday that 90 per cent of
Thibault's questionable expenditures had been paid to her by the federal government.
Thibault's successor, Pierre Duchesne, is working with the government to come up with tighter spending protocols for the province's lieutenant-governors.
The Parti Quebecois, meanwhile, is calling for the lieutenant-governor to make annual appearances before the legislature to justify expenditures.
The PQ's Sylvain Simard said there needs to be more transparency in the finances of the lieutenant-governor in the future.
Ottawa's Sheila Fraser and Quebec's Renaud Lachance said Thibault racked up $239,000 in personal expenses over the 10 years, including $3,700 on fishing trips and $4,000 on a reception to celebrate the birthday of one of Thibault's relatives.
Fraser and Lachance also said $129,000 was claimed from the federal government for accommodation and meal expenses already covered by Quebec.
Another $343,000 intended for expenses was used as supplementary pay, they said.
Pelletier noted Wednesday that the Quebec government stopped paying for Thibault's public relations when she was officially replaced last week by Duchesne.
