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 No10.
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.
Writing for The Daily Telegraph, Ms Truss has vowed to set out “immediate action on energy bills and energy supply” in her first week in office.
Ms Truss adds: “We need to take the difficult decisions to ensure we are not in this position every autumn and winter.
“Sticking plasters and kicking the can down the road will not do.”
Ms Truss also reveals that she will set up a “council of economic advisers”, comprising “a team of world-class economists, so my chancellor and I have the best ideas and latest research on how to get the economy moving”.
Previosuly, current Chancellor Nadhim Zahawi has insisted more support is on the way for the public and for businesses ahead of the surge in energy bills from October.
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.
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.