The Seraph's Watch, produced in 1847, was discovered by curator Julian Treuherz in a private collection in 2009.
It was last on public display in 1896.
The painting's existence was only known about because a copy was made by fellow artist Dante Gabriel Rossetti. That copy sold for £100,000 at auction in 2006.
If and when the original comes up for sale, we expect it to net a considerable sum.
A Michelangelo drawing, Study of a Mourning Woman, sold for £5.9m in 2001, having been discovered after 250 years of obscurity in Yorkshire, UK.
In 2009, a Ludovico Mazzolino artwork thought to have been lost, made £107,550 at Duke's auction house in Dorchester, UK. The 1522 piece far exceeded its £60,000 high estimate.
The work was found in a packing case by a British pensioner, having been forgotten for more than 60 years. It had last been sold for £20 in 1812.
Earlier this year, it was revealed that a depiction of the crucifixion hanging in a Jesuit student resident at Oxford University could be a Michelangelo.
The Seraph's Watch will go on display at Manchester Art Gallery from September 24 alongside 140 other pieces by Madox Brown.
One of two copies of his famous work The Last of England, which depicts two English emigrants, sold for £206,850 at Christie's in 2004.
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