Sunak was one of the first to resign, along with Health Secretary Sajid Javid, but Truss remained loyal to Johnson until the end.
Truss pipped trade minister Penny Mordaunt in the final round of MPs’ voting in July to make it through to face Sunak, but she proved more popular in 12 regional hustings than the former finance minister among the 172,000 grassroots Conservative Party members.
Voting closed on Friday and Sir Graham Brady, chairman of the 1922 Committee of Conservative backbench MPs, announced the result on Monday.
Truss won 81,326 votes, compared to 60,399 for Sunak.
The Co-chairman of the Conservative Party, Andrew Stephenson, praised Johnson who, he said, had “time and again rose to the challenge” from issues such as the COVID-19 pandemic and the war in Ukraine.
In a speech immediately after the result was announced, Truss paid tribute to Sunak and Johnson, who she said was “admired from Kiev to Carlisle.”
Truss Promises ‘Bold Plan to Cut Taxes and Grow the Economy’Truss said: “I will deliver a bold plan to cut taxes and grow the economy and I will deliver on energy bills.”
She also promised to deliver a “great victory” to the Conservative Party at the next election.
Sunak wrote on Twitter following the announcement: “I’ve said throughout that the Conservatives are one family. It’s right we now unite behind the new PM, Liz Truss, as she steers the country through difficult times.”
Usually the outgoing and incoming prime ministers go to Buckingham Palace to talk to the Queen, who is the head of state, but in a break from tradition they are expected to travel to Balmoral in Scotland on Tuesday to meet the monarch.
Scotland’s First Minister, Nicola Sturgeon, wrote on Twitter: “Congratulations to Liz Truss. Our political differences are deep, but I will seek to build a good working relationship with her as I did with last 3 PMs. She must now freeze energy bills for people & businesses, deliver more cash support, and increase funding for public services.”
Truss is understood to have largely finalised her new Cabinet and is expected to announce her new-look government on Tuesday evening.
But one of Sunak’s supporters, former chief whip Mark Harper, urged her to unite the party by picking people from different wings of the party.
In 2007, after becoming prime minister, Gordon Brown considered a snap election but decided against it and lost the general election two years later, after Britain was hit by a global financial crisis, while Theresa May opted for an election in 2017, a year after coming to power, but ended up losing her parliamentary majority.
The priority for Truss will be tackling Britain’s cost-of-living crisis and especially soaring energy bills.
Last week the regulator Ofgem said British households can expect their average energy bills to rise by 80 percent in October.
Truss Under Pressure Over Energy BillsTruss made tax cuts her main priority during her leadership campaign but she is coming under intense political pressure to offer consumers help with their energy bills.
Asked on Sunday by the BBC’s Laura Kuenssberg what she planned to do on energy bills, Truss said: “Before you have been elected as prime minister, you don’t have all the wherewithal to get the things done. This is why it will take a week to sort out the precise plans and make sure we are able to announce them. That is why I cannot go into details at this stage. It would be wrong.”
But she said she would announce a plan within a week of becoming prime minister.
The Republic of Ireland’s foreign affairs minister has said he hopes “the direction of travel” will change under Truss.