The 'Cornish Wonder' was born at St Agnes, near Redruth, the son of a woodworker and carpenter. He began his travels at the age of 15 as a travelling portrait painter under the patronage of his discoverer and tutor, the physician/artist, Dr William Wolcot, and moved around the county painting on commission to the leading merchant and banking families of the county.

Padstow, Penryn, Penzance, Fowey and Falmouth were all, in turn, visited, where he was commissioned to paint different studies as well. Sir Rose Price of Trengwainton, for example, having seen some of Opie's pictures of old men and beggars, commissioned him to paint An Aged Beggar as seen on the streets of Penzance. Amongst the early Opie patrons were the families of St Aubyn, Carne, Penwarne, Prideaux, Daniell, Vivian, Grylls, Rashleigh, Giddy and Scobell (7 portraits of the family at Nancealverne). He was also to paint the famed Cornish legendary people, Dolly Pentreath (last Cornish language speaker) and John Knill (of St Ives). A recent discovery has been made (in a midlands auction room) of a neglected portrait by Opie of a young Falmouth girl, Lydia Gwennap, who was later to become the wife and co-philanthropist with her husband John Broadley Wilson in Clapham, London, where their contributions 'to moral and reforming societies' came second only to William Wilberforce himself. [Carter, 2013]

Wolcot promoted his protegee's talents far and wide and took him to London in 1781, one of his earliest commissions being from the King for another famous Cornish connection, Mrs Delany. In London, even more than being 'The Cornish Wonder' Opie was hailed as the 'English Rembrandt'. From 1782 to 1807 he exhibited at the RA, gaining associate status then full Academy membership rapidly. He married twice, Mary Bunn (December, 1782), a young girl whom he had painted, and who he placed second to his work, and in 1798 to Amelia Alderson, a literary personage of merit, who outlived him and came to Cornwall in her own later years to pay her respects to his home country.

John Passmore EDWARDS gave the gift of the Newlyn Art Gallery to the artists in memory of John Opie, and upon occasion it has been called the Opie Gallery at Newlyn in accordance with the engraved plaque across the streetside front.