It will be offered at Cheffins with a £30,000-50,000 estimate at its auction on March 22-23.
Measuring 12¼ x 16½in (31 x 42cm), it shows the castle overlooking a wooden bridge across the River Wye and was executed by the 19-year-old artist following a tour of Wales.
Signed and dated 1794, it has been authenticated by art historian and Turner expert Andrew Wilton and its provenance has been traced back to Dr Thomas Monro, one of the artist’s most important patrons.
Having sold at Christie’s in 1917, seemingly its last public appearance, it has come to auction from a London-based vendor descended from George Cock Gibson (1896-1989) in whose family it has been since at least 1956.
The subject of Chepstow Castle and bridge was one of 16 scenes commissioned for John Walker’s ‘Copper-Plate Magazine’ from 1794-98 – the first time Turner was asked to supply a set of topographical views for a publication.
While no sketches of this composition are known, two pencil drawings of Chepstow from Turner’s trip to Wales in June-July 1792 can now be found at Tate Britain.
A smaller watercolour of the same view, but undated and less finished, is in the Courtauld Institute.