The painting will be on display at the National Portrait Gallery until January
The National Portrait Gallery in London has teamed up with a museum in Preston, Lancashire to buy a portrait of a giant of the Industrial Revolution.
The portrait of textile engineer Sir Richard Arkwright was last exhibited in 1883 and cost £420,000 to acquire.
It was the work of Joseph Wright of Derby, a leading 18th Century artist.
Independent art charity The Art Fund put £100,000 towards the purchase, with another £132,000 contributed by the National Heritage Memorial Fund.
Sandy Nairne, director of the National Portrait Gallery, described the artwork as "an outstanding acquisition of a great pioneer, painted by one of the finest of British portraitists."
The painting will alternate between the London gallery and the Harris Museum in Preston, the city where Arkwright was born in 1732.
The so-called 'Cotton King' invented a cotton-spinning water-frame that enabled the large-scale mechanisation of the industry.
He was knighted in 1786, the year after Joseph Wright of Derby completed his portrait.
David Barrie, director of The Art Fund, said the acquisition was "a real coup" for both galleries.
The portrait, he said, "perfectly captures the private side of a formidable character who helped shape modern Britain".
Carole Souter of the National Heritage Memorial Fund echoed those sentiments, saying she was "delighted" the work "will now belong forever to our nation".