Turkey's ruling AK Party is set to appoint a key ally of President Recep Tayyip Erdogan as its leader and new prime minister, after a reported rift led Ahmet Davutoglu to quit.
Binali Yildirim, the outgoing transport minister, is the sole candidate at a party congress in Ankara.
His main task will be to oversee constitutional changes to increase the president's power, correspondents say.
The issue is thought to have been behind the resignation of Mr Davutoglu.
The BBC's Mark Lowen in Istanbul says Mr Yildirim will not step out of line with Mr Erdogan and will even be ready to support a constitutional change that would see his role effectively scrapped.
Some Western leaders find Mr Erdogan hard to deal with, he says, and opponents believe an unchecked Mr Erdogan will clamp down further on dissent.
But Mr Erdogan's supporters - mainly conservative, pious Turks - still see him as the man who gave them a political voice and insist he is right to exert his control, our correspondent says.
Mr Yildirim takes the job as Turkey faces security threats from PKK Kurdish militants and so-called Islamic State.
A ceasefire between Turkey and the PKK ended weeks after elections in June 2015, and the renewed conflict has claimed hundreds of lives on both sides, particularly in Turkey's south-east.
In a speech on Thursday, Mr Yildirim made clear he would work "in total harmony" with the president and all other levels of the AKP.
Mr Davutoglu resigned two weeks ago after failing to reconcile his differences with Mr Erdogan.
Mr Davutoglu said he would continue as a party legislator and would not try to divide the AKP.
The choice of Binali Yildirim has surprised few in Turkey, as he has been an Erdogan favourite for years. He has remained loyal in the most troubling times, and that loyalty appears to have paid off.
He has served as transport minister for many years, and did not hesitate to resign from his post to run for the mayoral elections in the western city of Izmir, a secular stronghold, at Mr Erdogan's request.
His name had come up as a possible candidate for the party leadership at last year's AKP congress. And that forced Mr Davutoglu to concede some of his powers within the party.
One AKP MP had to apologise after suggesting that the next prime minister would be a "low-profile" name.