The Foreign Secretary won the backing of Defence Secretary Ben Wallace, who called her “authentic, honest and experienced” with the “integrity” for the top job.
He accused her leadership rival Rishi Sunak of trying to block “vital” defence money during his time as chancellor.
Asked during a visit to Norfolk on Friday if she was confident she was now set to win the leadership contest, Ms Truss said: “I’m not at all complacent. I’m fighting for every vote across the country.”
She added: “I’m delighted to have the support of Ben Wallace. We’ve worked very closely together. He’s been a fantastic defence secretary for our country.”
Meanwhile, in a thinly-veiled swipe at the former chancellor’s record, she warned it would be “risky” for the country to continue along the current economic path.
Ms Truss insisted the way to get growth is to “help people and businesses keep more of their own money”, saying the “number one priority should be avoiding recession”.
She said: “What is risky is carrying on on the same economic path, which is currently forecast to lead us to recession. That is the risk.
“What I’m talking about is unleashing opportunity, unleashing growth, keeping taxes low. That will see the economy grow, and it will see us being able to pay back our debt quicker.”
Ms Truss also committed to “challenging the current orthodoxy around investment spending”, with more going into “left-behind areas”.
In a series of interviews on Friday morning, Mr Wallace explained the reasons behind his support for Ms Truss, while also making veiled digs at Mr Sunak’s record in the Treasury.
His backing is seen as a major and further boost for Ms Truss, who has come out ahead in polls and surveys of Tory party members.
Mr Wallace told Sky News the Foreign Secretary recognises “the threats we face every day” need to be “funded properly”, pointing to Ms Truss’s commitment to increase defence spending to 3 per cent of GDP by 2030.
He also said that without any prompting or asking, Ms Truss wrote a letter to the Prime Minister saying that defence needs more money.
In contrast, Mr Sunak, the Defence Secretary said, tried to block “vital” defence money in 2019, only to find himself overruled by the Prime Minister.
Mr Wallace was asked by LBC’s Nick Ferrari how obstructive the former chancellor was in granting more cash to the armed forces.
He replied: “I don’t think he was obstructive…”
When pressed further, the Defence Secretary said: “I mean, the multi-year settlement that we got was not what the Treasury had wanted.
“They wanted a one-year settlement. This was back in 2019, I think. It was vital that we got a multi-year settlement.
“The Prime Minister effectively asserted his authority and made sure that’s what happened.”
Mr Ferrari asked: “But Mr Sunak was not in support?”
Mr Wallace said: “Not that I remember.”
Speaking to BBC Breakfast, the Defence Secretary insisted Mr Sunak would be a “fine member of anybody’s Cabinet”, but added: “For me, Liz is the one that I think will do best by defence of this nation, by investing in it.
“When I was in Government, without any prompting or asking, Liz, I remember, wrote a letter to the Prime Minister saying that defence needs more money, it’s a more dangerous, risky world.
“She did that off her own back. She’s been very consistent.”
Mr Wallace also criticised Mr Sunak’s resignation, which played a key role in Boris Johnson’s downfall.
He told Sky News: “I just don’t think triggering Cabinet ministers walking out at a time of a crisis is the right course of action.
“There were other mechanisms to do what they wanted. If Rishi Sunak didn’t want the Prime Minister to be Prime Minister, there are other mechanisms to do that. And that goes for all the other ministers.”
He described Ms Truss as “a winner not because she’s a slick salesperson, but because she is authentic”.
It came after Ms Truss and Mr Sunak faced a grilling from voters on Thursday evening in the first official hustings with Conservative Party members in Leeds.
The event, hosted by Mr Ferrari, was the first of 12 sessions for the party faithful across the country to question the final two contenders, before voting for the next Tory leader and prime minister closes on September 2.
While they did not address one another directly, tax continued to be a significant dividing line between the pair.
Mr Sunak said he would not “embark on a spree, borrowing tens and tens of billions of pounds of unfunded promises and put them on the country’s credit card”.
Meanwhile, Ms Truss criticised windfall taxes – something Mr Sunak imposed as a one-off on energy companies as chancellor.
She said: “I don’t believe in windfall taxes because they put off future investment.
“What we should be doing is encouraging Shell and other companies to invest in the United Kingdom, because we need to get our productivity up, we need capital investment.”
The former chancellor acknowledged he is trailing Ms Truss in the polls, but vowed to fight for every vote.
He said: “We are going to have to appeal to swing voters in every part of our country. And I believe with all my heart that I am the person, I am the candidate, that gives our party the best opportunity to secure that victory.”
He later denied that his pledge to cut VAT on energy bills was a U-turn.
Mr Sunak was due to face veteran political journalist Andrew Neil for a crunch interview on Friday – an opportunity Channel 4 said Ms Truss had declined earlier in the week.