The work by Sir David Wilkie surfaced at an auction house in New York and was snapped up by a British art dealer for a fraction of what it is worth because the artist was unidentified.
The Fife-born artist’s painting will now go on sale during London Art Week and is expected to go for more than £250,000.
London-based dealer Ben Elwes said he recognised Wilkie’s work immediately in a sale catalogue and flew out to New York to see the painting.
It was known to exist because it had featured in sketches of eight of paintings Wilkie had sent to his brother while serving in the army in India.
Mr Elwes said the work had been verified as that of Wilkie by art historian Hamish Miles, Britain’s foremost expert on the artist who is heavily featured in the collections of the National Galleries of Scotland.
Wilkie’s portrait, of a young woman kneeling at a prayer desk, was last heard of in 1872 when it was put up for sale by a relative of a former Tory MP, whose daughter is thought to be the subject of the painting.
Wilkie, a minister’s son who went on to become one of Britain’s first artists to enjoy significant success overseas, made his name painting various images of rural life in Fife.
The missing painting is described as a “tour de force” by the organisers of London Art Week. It is thought to have been painted in 1813.
The main figure is believed to be Augusta Phipps, a daughter of the first Earl of Mulgrave, Henry Phipps, a general who went on to serve as foreign secretary under William Pitt the Younger.
Mr Elwes, whose gallery, Ben Elwes Fine Art, will be putting the painting on display from 4-11 July, said: “I’d rather not say what I paid for it, but it was significantly below what it is worth. It’s probably the most significant discovery I’ve made.
“He is a hugely significant figure in Scottish and British art, but was also very influential in Europe. He was up there with Turner and Constable.
“We know his work very well, but it is rare to come across one of his paintings.
“He died relatively young and, as he was the king’s official painter, a lot of his work is in the royal art collection and is not likely to ever leave it.”
A spokeswoman for London Art Week said: “Wilkie is considered to be the first truly international British artist. Unlike any of his forebears, he was patronised by great collectors and royal households across Europe during his lifetime.
“This painting by Wilkie shows the artist at the peak of his powers when he is creating his own unique and personal visual vocabulary which was to have such a profound effect on both British and continental painting later in the century.”
Wilkie was born in 1785 in the Fife village of Cults – the place which was to inspire much of his work. He studied at the Trustees Academy in Edinburgh and, after a brief period working in Fife, found huge success after moving to London.