Liz Truss will become the next prime minister of the United Kingdom after winning the most votes in the Conservative Party leadership contest, replacing Boris Johnson who resigned in July after a series of scandals.

Truss beat rival Rishi Sunak by 81,326 votes to 60,399 among party members and will take over as leader on Tuesday, as Britons grapple with economic and social crises.

She promised action to tackle the crisis in a brief victory speech at a London conference center on Monday.

Truss has been leading for weeks, and the 47-year-old will now follow Margaret Thatcher and Theresa May to become Britain's third female prime minister.

Despite voting to remain in the European Union in 2016, he found himself the preferred candidate of most Brexiters in his party.

Liz Truss's victory was narrower than expected, as conservatives backing both candidates privately acknowledge.