While Britain was better placed to cope with economic shocks compared with 2008, it was "not immune to what's going on", he said.
"My message in this Budget is that the world is a more uncertain place than at any time since the financial crisis and we need to act now so we don't pay later," he said.
"That is why I need to find additional savings equivalent to 50p in every £100 the government spends by the end of the decade, because we've got to live within our means to stay secure.
"That's the way we make Britain fit for the future."
The chancellor - whose Budget on Wednesday will be his eighth - said he thought the savings were achievable, but he would not be drawn on where the axe would fall.
He said the government's plan had enabled it to invest in "the public's priorities", such as the NHS, science and education, infrastructure and defence, "while at the same time not spending more than the country can afford".
Mr Osborne added that he wanted to boost productivity, improve Britain's schools and infrastructure and make taxes "more competitive".
The chancellor declined to be drawn on whether fuel duty would be increased - something Tory backbenchers are urging him against.
Image copyright PA Image caption Conservative MPs are campaigning against any rise in the price of petrol
But he added: "On fuel duty, we had a manifesto commitment there and we have pencilled in fuel duty plans going forward but what I would say is, every time we can have our economy more competitive, we do."
Mr Osborne also rejected claims that the most vulnerable people would be hit in the Budget through cuts to disability benefits known as Personal Independence Payments (PIP).
He said the government was "increasing spending on disabled people", but added that it was right to make sure the system was being "properly managed".
Also on Marr, Labour's shadow chancellor John McDonnell called for more long-term investment in the UK economy, specifically in skills, infrastructure and new technology.
He said the chancellor had reduced investment to 1.4% of GDP which was "unacceptable", saying the OECD has said the figure should be at least 3%.
Media captionShadow chancellor John McDonnell calls for more long-term investment
"What I want to do is to make sure we invest in the long term and then we can withstand the global headwinds," he added.
He said prosperity needed to be "shared by all", saying the government's economic policies had created an "unequal" society.
The chancellor has promised to get the books into surplus by 2020.
In his November Autumn Statement, he watered down planned £4.4bn cuts to tax credits and eased back on planned spending cuts to the Home Office and other departments. He was able to do this owing to a combination of better tax receipts and lower interest payments on debt.
BBC political correspondent Eleanor Garnier said: "Only four months ago, when he made the Autumn Statement, Mr Osborne had sounded upbeat about the country's finances.
"But now, with the size of the British economy much smaller than had been expected, it seems the chancellor has not left himself much wriggle room."
'On the stomp'
In his Marr interview, Mr Osborne also touched on the upcoming in-out referendum on the UK's EU membership, warning that a vote to leave "would create an economic shock" that would "cost jobs" and "damage living standards".
He said Turkey becoming a member of the EU was not "on the cards any time soon", raising the prospect of the UK vetoing its accession.
"We can set conditions and we have made it absolutely clear that we will not accept new member states to the European Union and give them unfettered free movement of people unless their economies are much closer in size and prosperity to ours," he said.
His comments come after a proposed deal between the EU and Turkey which would see Turkey take back migrants who reach Greece in return for more EU funding, a relaxation of visa requirements for Turkish nationals and faster progress on accession talks.
London mayor Boris Johnson, who is one of a number of senior Conservatives backing the Vote Leave campaign, said he was "very dubious" about the proposed deal.
"I am certainly very dubious on the other side of the coin about having a huge free travel zone. I think that is one of the problems, that we need to take back control of our borders," he said.
He also argued that the UK was "big enough and strong enough to stand on its own", saying the EU costs the UK "a huge amount of money and subverts our democracy".
Mr McDonnell told the Marr show he and the Labour shadow cabinet would be "on the stomp" campaigning for the UK to stay in the EU amid criticism Labour has been quiet in the campaign.
He said the EU needed reform to make it more "transparent" and "democratic" but argued that Britain was better able to do that from within the bloc.