Writing in the IMF's new World Economic Outlook, Maurice Obstfeldt said "we could be at a turning point".
The report forecasts global growth this year of 3.5%, up from 3.1% predicted in 2016.
The UK's economy is forecast to expand by 2% this year, stronger growth than any of the major developed economies apart from the US.
The prediction for Britain this year is now only marginally below what the IMF predicted a year ago, its last full forecast before the Brexit referendum.
The figure then was 2.2%. The revised forecast reinforces the picture of the British economy's performance being little affected by the aftermath of the referendum, contrary to the expectations of the IMF and many independent economists. The IMF does, however, expect the longer term impact on Britain to be adverse.
The IMF also warns of headwinds that could weaken its global projections. The organisation highlights the possibility of protectionism and what the report calls "trade warfare".
However, the dominant tone of the report is rather sunnier than it has been for some time. For much of the period since the financial crisis of 2008 the IMF has worried that the recovery was failing to generate momentum.
This time the IMF sees buoyant financial markets and "a long awaited cyclical recovery in manufacturing and trade".
The rebound in the prices of commodities has also helped dispel fears of deflation, or falling prices, which has been seen as a danger, especially in the developed world. Deflation can, in some circumstances, aggravate economic weakness.
The forecast for this year would be a marked improvement on last year's 3.1%.
It's striking that in the forecast for the larger economies, there are none predicted to suffer a decline in economic activity this year or next.
Even Brazil and Russia, two countries that have suffered from the fallout of international and domestic political difficulties, are forecast to see growth this year, although it's not particularly strong.
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Inevitably, the IMF identifies possible risks that could weaken its main forecasts. In particular, the report refers to increasing "pressures for inward looking policies in the advanced economies".
The report notes the loss of what it calls middle-skilled jobs in advanced economies as a result of technological change since the early 1990s. There is controversy about to what extent increased global trade might have contributed to those losses.
Combined with the slow recovery from recent economic crises, this has affected people on lower incomes and led to growing disillusionment with globalisation the, IMF says.
The report warns that this could trigger more protectionist policy actions on trade and immigration.
Mr Obstfeldt writes: "Capitulating to those pressures would result in a self-inflicted wound, leading to higher prices for consumers and businesses, lower productivity, and therefore, lower overall real income for households."
The report also says that the increased fragmentation of production processes across countries aggravates the potential economic damage.
The forecast for Britain has been revised up markedly for this year - to growth of 2%, from 1.6% predicted in 2016. That is a stronger than any of the leading developed economies apart from the US, whose growth is forecast to be 2.3%.
The revision for the UK reflects what the report calls the "stronger-than-expected performance of the UK economy since the June Brexit vote".
But the IMF still expects negative effects from leaving the EU including "reduced consumer purchasing power following the pound's depreciation and its gradual pass-through to prices and the impact of uncertainty on private investment".
It also says that longer term prospects have been diminished because of the expected increase in barriers to trade and migration and the potential impact on the UK's financial services.
One decidedly weak area is Africa, for which the IMF describes the outlook as subdued. For sub-Saharan Africa, economic growth is likely to only moderately exceed population growth. That means correspondingly only moderate progress in raising average living standards in the region.
Although commodity prices such as oil have rebounded from recent troughs, they are still relatively low. The Fund says that is holding back growth in oil-producing nations in Africa such as Nigeria and Angola.
Source: BBC News