Jeremy Corbyn says the government's response to coronavirus proves he was "absolutely right" about public spending at the 2019 general election.
The Labour leader told the BBC he had been "denounced as somebody that wanted to spend more money than we could possibly afford" to fix social wrongs.
But he said he had been vindicated by the vast sums the government was spending on the current crisis.
The Tories now realised they had to "invest in the state", he added.
In an interview with BBC's Political Editor Laura Kuenssberg, Mr Corbyn said that the country had been "ill-prepared" for the coronavirus pandemic because of "10 years of austerity, of underfunding the National Health Service and underfunding our benefit system".
He said the government had been "shocked" by the national emergency, as their "instincts" were for "free market economics and the small state".
"They've now suddenly realised that they have to spend money to invest in the state, as we have always said as a party, and they have come around to a lot of that position."
'We need everybody'
Mr Corbyn said the government had also failed to realise how many people were in "insecure" employment in the UK when they drew up their response to the emergency.
But he believed that the pandemic had changed the political landscape forever.
"I think our society and our politics will never be the same again, because we have suddenly realised as a society and a community, we need everybody - and everybody has a contribution to make."
Mr Corbyn has just over a week to go as Labour leader, after four-and-half years in the job.
The result of the contest to replace him - between Sir Keir Starmer, Rebecca Long-Bailey and Lisa Nandy - will be announced on Saturday, 4 April.
Mr Corbyn decided to stand down after Labour's heavy defeat in December's general election, which came two years after a narrower defeat at the polls.
He said: "I did everything I possibly could to win both elections and to say to the people of this country, the only way our society can come together is if we're prepared to invest.
"I was denounced as somebody that wanted to spend more money than we could possibly afford, in order to right the social wrongs of this country.
"I didn't think that it would take only three months for me to be proved absolutely right by the amount of money that government is now prepared to put in - and Parliament has just voted through - to deal with the coronavirus crisis.
"So this is a change in our politics, which the coronavirus crisis has actually meant in every country in the world.
"There's suddenly a realisation that we're only as healthy as the safety of our neighbour."
Labour fought the 2019 election on a promise to increase spending on the NHS and other public services and bring rail, water, electricity and broadband into public ownership.
Mr Corbyn blamed the party's defeat on divisions over Brexit, which led to a vote at Labour's conference to negotiate a new deal with the EU and then put it to another referendum.
That policy "clearly did not win the election", Mr Corbyn told Laura Kuenssberg.
But he added: "I did my best to bring people together on the principles that in or out of the EU, we needed to have an investment-led economy, we needed to be anti-austerity."
Asked if his leadership was also to blame, he said he had received "unprecedented level of abuse from the mainstream media of me personally", which he said had to be "factored in".
Reflecting on his time as leader, he said was "proud" of Labour's "hugely expanded membership" and that he had been able to shift the party towards an "interventionist" economic policy and opposition to austerity, as well as its plan for a "green industrial revolution".
He was "desperately sad" about losing the 2019 election, in particular, but he believed the party was making an important contribution to the "national debate".
Asked if he had made any mistakes as leader, he said: "Of course! I'm a human. Of course I've made mistakes."
He said he had made appointments to his team that did not "work out".
"You give faith in people that don't necessarily return it too well, and you sometimes make judgement mistakes. We all do."
Asked if he had any advice for his successor, he said: "Spend time listening to people in all parts of the country, travel as much as you can around the country as I have done."
And he urged whoever takes over the reins to "recognise the strengths and the good in people, and that we can bring about a decent better society in the great traditions of socialism and the Labour Party".