Truss, who is currently Britain's foreign minister, beat former finance minister Sunak in a vote of Conservative Party members with a margin of 20,927 votes.
"I will deliver a bold plan to cut taxes and grow our economy. I will deliver on the energy crisis, dealing with people's energy bills, but also dealing with the long-term issues we have on energy supply," Reuters quoted Truss as saying after the announcement of the result.
Sunak, separately, thanked everyone who voted for him in the campaign. "I have said throughout that the Conservatives are one family. It is right we now unite behind the new PM Liz Truss as she steers the country through difficult times," he said in the tweet.
It merits mentioning here that the United Kingdom is facing a crunch on household finances, industrial unrest, a recession and war in Europe, with the country being a leading supporter of Ukraine.