Born at Thrussington in Leicestershire, the son of a wheelwright, John Ferneley was first apprenticed to his father's trade. His artistic talent was soon recognised by the Duke of Rutland, who admired some of his pictures which adorned a cart on which his father was working. In 1803, at the instigation of the Duke of Rutland, Ferneley was sent to London to study with the successful sporting painter Benjamin Marshall; he also enrolled at the Royal Academy Schools and exhibited at the Royal Academy from 1806 to 1853.
From 1804, John Ferneley travelled extensively around England, visiting Dover (to paint the Leicestershire militia), Norfolk and Lincoln. In 1808 he went to Ireland, where he returned annually between 1810 and 1812, painting many pictures for the Irish gentry.
Ferneley spent the rest of his life at Melton Mowbray in Leicestershire, where he built a studio and house named Elgin Lodge. His reputation earned him the patronage and friendship of many Meltonians and members of the aristocracy. Ferneley was patronised by some of the most fashionable figures of the day, including Beau Brummel and Count d'Orsay.