Brown won the leadership of the Ontario PC Party on Saturday, besting the veteran MPP Christine Elliott in the contest for the job.
The CBC's Mike Crawley reported Sunday that Brown will formally resign from his federal seat Wednesday after Question Period.
Brown has represented the riding of Barrie since he was first elected to Parliament in January 2006. He was re-elected two more times as the MP.
The new PC leader has yet to say when he'll try to win a seat in the Ontario legislature.