The think tank said borrowing was likely to rise to £100bn and total debt would soar to 90% of national income.
The research was part of IFS's Green Budget annual assessment of public finances, published as chancellor Sajid Javid gears up to deliver his first Budget this autumn.
Government debt is set to rocket to levels not seen since the 1960s in the event of a no-deal Brexit, a leading economic think tank has warned.
It said the Government's day-to-day spending plans for public services were now close to the levels implied by Labour's 2017 election manifesto, and far higher than those in the Conservative manifesto.
It will continue to closely monitor the effects of the temporary tariff regime on the United Kingdom economy and has announced an exceptional review process will be used to make changes to the temporary tariff regime if necessary after exit day.
French president Emmanuel Macron told United Kingdom prime minister Boris Johnson that the remaining 27 European Union members will make their decision by the end of the week after they discuss whether a proposed Brexit deal can "respect" the bloc's principles and is likely to be passed through parliament.
In the case of a no-deal Brexit, it should implement "carefully targeted and temporary tax cuts and spending increases where it can effectively support the economy", he said. "In so doing, we will retain a fiscal anchor to public spending so that decisions are taken with a view to the long-term sustainability of the public finances".
Prime minister Boris Johnson has also emphasised the importance of government spending programmes being temporary, should the economy not perform as well as expected.
The body stated that "securing a Brexit deal would be better for the economy over the next two to three years than another delay", adding that "some pent-up investment should occur, and consumer confidence would improve, as the risk of a no-deal Brexit recedes".
He said that in the event of no-deal, any measures to support the economy would have to be strictly temporary.
This idea is supported by Christian Schulz, the leading United Kingdom economist at Citi, one of the leading firms which helped produce the IFS report. If this were to come with tax cuts and further spending increases together worth 1 to 1½% of GDP (over and above the loosening at the September 2019 Spending Round), then growth should pick up to (a still poor) 1½% a year in the short term.
Even if Brexit were called off, the flatlining of business investment in theUnited Kingdom over the past three years would be hard to unwind, Schulz said at a media briefing on Tuesday.
"From a growth perspective, a Brexit deal is a little better, leaving growth at 1.5 per cent, but it would leave no chance of Brexit being cancelled".