Education Minister Adrian Piccoli and Hospitality Minister Troy Grant are expected to face off in the ballot on Thursday morning to install a party leader.

Mr Stoner said his "difficult" decision to retire followed a request from his wife Cathy, who is dealing with serious "health issues".

He will step down as Nationals leader on Thursday morning but will remain in cabinet overseeing his portfolios, which include trade and investment, tourism and major events, until the election next year.

The member for the mid-north coast seat of Oxley, Mr Stoner has served in the NSW Parliament since 1999 and as Nationals leader since 2003.

He said the decision to retire from Parliament was made after a recent break with his wife and three children.

"I became aware of the seriousness of the issues with which my wife has been dealing," he said.

"She asked me to bring forward my plans for retirement and I didn't hesitate."

Mr Stoner his wife has been dealing with "some health issues and other issues".

He pointed out that last year the job meant he spent 250 days away from home.

"This has coincided with some very difficult family issues that have been faced by my wife and three children back at home," he said.

"I can no longer expect or ask my wife, Cathy, to face these issues alone".

Mr Stoner said he has "no job lined up, I'm not under any cloud. This is about putting my family first".

He said he could not see himself taking on full-time employment upon leaving politics but would consider part-time work.

Premier Mike Baird said Mr Stoner had been "a great leader of the NSW Nationals, a fine Deputy Premier and above all a passionate advocate for regional NSW".

Nationals state chairman Bede Bourke said Mr Stoner had been "a steady and patient hand at the wheel at a critical time in our history. He has served the people of NSW and the members of the Nationals with distinction, and I wish him and Cathy well in his retirement."