Caroline Drolet said in Quebec City on Tuesday today her client will enter a guilty plea to fraud and breach of trust charges on June 5, when sentencing arguments begin.
His trial had been set to begin June 2.
The 43-year-old Tomassi faces up to five years in prison.
The ex-family minister was forced to resign in 2010 after reports surfaced he had been using a credit card provided by a company that received millions in government grants.
The charges related to allegations Tomassi received material rewards from the company between 2006 and 2010.