Bentley confirmed Friday that he is leaving cabinet and is resigning his seat effective next Thursday.
That means incoming Premier Kathleen Wynne will have to call a byelection for his London West seat, as well as for outgoing Finance Minister Dwight Duncan's seat in Windsor-Tecumseh.
Bentley was caught in the controversy surrounding the Liberal government's decision to cancel gas plants in Oakville and Mississauga in the midst of the 2011 election campaign.
Bentley was not energy minister at the time, but became the target of opposition attacks when he assumed the portfolio after the election.
Wynne and her new cabinet will be sworn in on Monday.