While the winner of the Tory leadership race will not be announced until Monday, the Foreign Secretary is widely expected to defeat former chancellor Rishi Sunak to take the keys to Number 10.
Newspaper reports late on Saturday focused on the immediate preparations taking place behind the scenes, with Ms Truss set to inherit an unenviable set of challenges.
The new prime minister will immediately face calls to tackle the energy crisis, amid increasing demands that the Government urgently intervenes to support households this winter.
The energy crisis, according to the Sunday Times, will be the focus of Ms Truss’ address from Downing Street once appointed.
The paper reports it is expected to be “very short”, but that an announcement on energy will come quickly once Ms Truss takes charge with a “fiscal event” set to take place in the coming weeks.
She has so far indicated that she would offer fresh support for households, but has given little detail about the exact form it might take.
Throughout the campaign she has pledged to “start cutting taxes from day one” with a new Budget and Spending Review that would reverse April’s rise in National Insurance and next year’s corporation tax increase from 19% to 25%.
Recent days have been full of speculation about who could make up the Cabinet in a Truss administration, with Business Secretary Kwasi Kwarteng among those tipped for high office.
There is also a growing expectation that the next prime minister will make an early visit to Kyiv to shore up support for Ukraine.
It comes as Mr Johnson prepares to leave office with praise from Volodymyr Zelensky ringing in his ears.
This is the moment for every Conservative to come together – and back that new leader wholeheartedly
Prime Minister Boris Johnson
The Ukrainian leader, writing in the Mail on Sunday, called the outgoing prime minister a “true friend” as he paid tribute to his steadfast support for the war-torn country.
Mr Johnson used his own article in the Sunday Express to reflect on his achievements, while also urging his party to come together after a summer of in-fighting.
“This is the moment for every Conservative to come together – and back that new leader wholeheartedly.
“This is the time to put aside the disagreements of the last few weeks, fascinating though they may have been, and put the national interest first.”
“As I leave Number Ten after three tough but often exhilarating years I know just how big and demanding this job is. I also know that either candidate is more than capable of delivering for the people of this country,” he wrote.
In what is set to be a frenzied few days for UK politics, Mr Johnson’s successor will be announced on Monday, taking over as prime minister the following day.
Mr Johnson and his successor will go to Balmoral, rather than Buckingham Palace, for the appointment of the new prime minister on Tuesday, in a break from tradition.
The Queen will receive Mr Johnson on Tuesday at her Aberdeenshire home, where he will formally tender his resignation.
This will be followed by an audience with the new Tory leader, where she or he will be invited to form a government.