The unsigned Dutch portrait, known as The Vegetable Seller, depicts a woman encircled by fresh produce.
The results of the restoration were uncovered by English Heritage on Friday, as it has been returned to the Audley End House in Essex for the first time in 60 years.
The restoration process saw the removal of a strip of canvas, which was found to have been added to the top of the painting in the late 18th or early 19th century, along with an addition of an upturned smile.
“The smile is such a change. She looks a lot more confronting I think, more serious,” English Heritage’s collections conservator Alice Tate-Harte told The Guardian.
They also unveiled “possible associations” between the painting and Flemish painter Joachim Beuckelaer, and have speculated that it may have been painted by the artist himself.
Beuckelaer’s work features in collections at the Prado museum in Madrid and The National Gallery in London.
“We’re so pleased that visitors to Audley End will now be able to see such a wonderful painting restored to its former glory,” English Heritage said in a statement.
The refreshed Vegetable Seller will be on view to the public at Audley End House from today (16 July).