Perreault was elected with more than 50 per cent of the vote in the Quebec riding of Montcalm in 2011 as part of the NDP wave in the province.
Her lawyer, Jean-Pierre Rancourt, said immediately after Friday's verdict in Joliette, northeast of Montreal, that he will appeal.
The 49-year-old Perreault was charged after she falsely accused a former employee of theft.
She was suspended from caucus last June and has since been sitting as an Independent.
A source within the NDP said Perreault will not return to the party.
"Madame Perreault was excluded from caucus when the charges were laid," the source said. "Today's judgment confirms this expulsion."
Rancourt said in an interview he will seek an absolute discharge for his client.
"It's a summary offence in the Criminal Code and, if she has a judicial file, she will lose her job."
She is to return to court on May 21, when she is expected to be sentenced.
Perreault's biography says she began her career as an administrator, working for Montreal-based financial institutions.
Perreault, who uses a wheelchair, was also a trainer with Keroul, an organization promoting tourism for people with disabilities.
She sat on municipal council in Sainte-Marie-Salome from 2002 to 2009.
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