Gladys Berejiklian has been elected leader of the NSW Liberal Party and will be sworn in as the state's 45th Premier.

At a Liberal party room meeting on Monday morning, Ms Berejiklian, 46, was elected unanimously, four days after Premier Mike Baird announced he was retiring from politics.

Finance Minister Dominic Perrottet was elected deputy Liberal leader and is likely to become Treasurer in a forthcoming reshuffle.

According to sources present, Ms Berejiklian told her colleagues that, unlike the Labor Party, which only appoints women to the top job when desperate and staring at electoral defeat, "we are promoting on merit".