While Tory MPs continue to disagree over his position, Ms Truss told reporters during a visit to Australia that Mr Johnson “100%” has her support and she wants him to “continue as long as possible in his job”.
Speaking at the Australia-United Kingdom Ministerial Consultations (Aukmin) in Sydney, she said: “The Prime Minister has my 100% support.
“He is doing an excellent job. Britain was one of the first countries to roll out the Covid vaccine.
“We’ve had a very successful booster programme. We’re now able to open up our economy again in Britain and we’ve got one of the fastest-growing economies in the G7.
“And the reason that we are here in Australia is working with our very close partners, to advance freedom and democracy around the world, and to protect our country.
“I want the Prime Minister to continue as long as possible in his job. He is doing a fantastic job. There is no leadership election.”
This comes amid more infighting within the Conservative Party as reports suggested rebel Tory MPs are considering publishing a secret recording and text messages linked to allegations of “blackmail” from the Prime Minister’s supporters.
Mr Johnson insisted on Thursday he had “seen no evidence” to support the claim made by senior Conservative William Wragg that his critics were facing “intimidation” as part of an effort to prevent him being ousted from office.
But The Times reported that Tory MPs keen to see the back of Mr Johnson have secretly recorded “heated” conversation with the chief whip, as well as text messages to support the accusations.
It comes as Sue Gray, the senior official leading an inquiry into claims of rule-busting gatherings across Government, was said to have found an email warning Mr Johnson’s principal private secretary Martin Reynolds against holding a drinks party in the No 10 garden during the first lockdown.
The email, sent by a senior official, told Mr Reynolds that the gathering “should be cancelled because it broke the rules”, according to ITV News.
Mr Johnson has admitted attending the gathering in question for 25 minutes on May 20 2020, but insisted he believed it was a work event, and that he was not warned it would be against the rules.
The PM has been battling claims that Tory critics are facing “intimidation” which could amount to blackmail as part of an effort to keep him in post.
Mr Wragg said on Thursday he had received reports of conduct including “members of staff at 10 Downing Street, special advisers, Government ministers and others encouraging the publication of stories in the press seeking to embarrass those who they suspect of lacking confidence in the Prime Minister”.
“The intimidation of a Member of Parliament is a serious matter. Reports of which I am aware would seem to constitute blackmail,” the chairman of the Commons Public Administration and Constitutional Affairs Committee said.
“As such it would be my general advice to colleagues to report these matters to the Speaker of the House of Commons and the Commissioner of the Metropolitan Police.”
But Mr Johnson, on a visit to Taunton, said: “I’ve seen no evidence, heard no evidence, to support any of those allegations.”
He said he would “of course” look for evidence to support the claims, but No 10 suggested there were no plans to launch an investigation as demanded by Labour.
The Times reported that one Tory MP said they were told by a whip “you’re done” when voting against the Government last year.
The paper also claimed Tory rebels met on Thursday to discuss their next steps.
Mr Wragg is one of a handful of Tory backbenchers to have said publicly they have submitted a letter to the chairman of the backbench 1922 Committee, Sir Graham Brady, calling for a no-confidence vote in Mr Johnson’s leadership.
He said the conduct of the Government Whips’ Office threatening to withdraw public funding from MPs’ constituencies may have breached the ministerial code.
Christian Wakeford, the MP who defected from the Tories to Labour in protest at Mr Johnson’s leadership and the row over Downing Street parties, said he was threatened about the loss of a school in his constituency if he did not toe the line.
The Metropolitan Police said they would consider any complaints made to officers.
“As with any such allegations, should a criminal offence be reported to the Met, it would be considered,” a spokesman said.
On the reports Ms Gray had found an email warning Mr Reynolds against holding a Downing Street drinks party, No 10 said it would not comment on the process of the ongoing investigation.