The verdict was handed down by Judge Denis Lavergne this morning in Montreal, convicting him of fraud relating to tens of thousands of dollars in inflated expenses, and fabricating fake documents.
Dupuis is the former head of the Quebec Federation of Labour's construction wing.
Dupuis pleaded not guilty to offences between December 2007 and November 2008, a period in which he filed 43 expense accounts totalling $225,000.
For example, he requested reimbursement for dining at six restaurants, for a total of $60,000.
One of those meals took place on December 30, while FTQ-Construction was closed for the Christmas holidays.
The meal cost $1,500 and included two bottles of wine at nearly $300 each.
At the Charbonneau corruption inquiry, links were made between Dupuis and several members of the Montreal Mafia, with their names appearing on the backs of invoices for restaurants he frequented.