The work by Baldassare Peruzzi is one of only a handful of his paintings known to be in existence.
A contemporary of celebrated artists Raphael and Michelangelo, he was a central figure of what became known as the High Renaissance around the early 1500s.
The work had been in a private collection in Britain for decades before being put up for sale.
Such is its cultural significance that the authorities put a temporary export ban in place to give domestic galleries and museums time to raise the asking price.
The Ulster Museum had just six months to raise the capital needed and was supported by several funders, including a grant of £70,000 from Stormont's Department of Communities.
Senior Curator of Art Anne Stewart said it was the perfect time to put the painting on display.
Ms Stewart: "Most of Peruzzi’s work was in fresco and much has been lost.
"His oil paintings are extremely rare and so it’s something of a Christmas miracle that we are able to welcome visitors to the Ulster Museum to enjoy this exciting new acquisition."
She said the biggest challenge of the period was in painting a night-time scene and Peruzzi had demonstrated great skill in the complex use of light to bring the work alive.
It is on display after months of careful restoration in London.