Former Montreal police chief Jacques Duchesneau says he won't run again for the party when the next election is called.
"I came into politics because of idealism," he said, adding he felt that he had given what he had to offer.
He told a news conference in Quebec City Wednesday afternoon he had promised to run for one term and that staying longer would cause family problems.
Duchesneau was elected at the last election, in September 2012.
He acknowledged Wednesday that his party had since slipped in popularity but said he believed it had a good platform.
Duchesneau gained a reputation for blowing the whistle on corruption in the province.
Premier Pauline Marois is expected to call a mid-April election within weeks. The Coalition has 18 seats in the 125-seat national assembly and sits a distant third in public opinion polls behind the Parti Quebecois and the Liberals.
Coalition Leader Francois Legault praised Duchesneau, saying he gave him valuable advice.
Duchesneau has also worked in the anti-collusion unit of the Quebec Transport Department as well as heading the Canadian Air Transport Security Authority before going into politics.