His series of paintings on the theme of a lion attacking a horse are early and significant examples of the Romantic movement that emerged in the late 18th century.

[2][3] While initially resistant, Stubbs's father (who died not long afterward in 1741), eventually acquiesced in his son's choice of a career path, on the condition that he could find an appropriate mentor.

[3] Stubbs subsequently approached the Lancashire painter and engraver Hamlet Winstanley, and was briefly engaged by him in a sort of apprenticeship relationship, probably not more than several weeks in duration.

[7] Forty years later he told Ozias Humphry that his motive for going to Italy was, "to convince himself that nature was and is always superior to art whether Greek or Roman, and having renewed this conviction he immediately resolved upon returning home".

In 1756 he rented a farmhouse in the village of Horkstow, Lincolnshire, and spent 18 months dissecting horses, assisted by his common-law wife, Mary Spencer.

Even before his book was published, Stubbs's drawings were seen by leading aristocratic patrons, who recognised that his work was more accurate than that of earlier horse painters such as James Seymour, Peter Tillemans and John Wootton.

A famous work, Whistlejacket, a painting of the thoroughbred race horse rising on his hind legs, commissioned by the 2nd Marquess of Rockingham, is now in the National Gallery in London.

His last project, begun in 1795, was A comparative anatomical exposition of the structure of the human body with that of a tiger and a common fowl, fifteen engravings from which appeared between 1804 and 1806.

Stubbs began an informal series of works on the subject of a lion attacking a horse around 1762 or 1763, and he continued to explore and reinterpret the theme in at least 17 images over a period of about 30 years.

[13]: 585 p. [14]: 109 p.  Jean Clay, professor of art history at the University of Paris, perceptively observed that not only does the energy and terror of the animals foreshadow the spirit of romanticism but, as Stubbs's series progressed, the horror seemed to diffuse and expand throughout the whole of the landscape: "an image that would fertilize the Romantic imagination and come to full flower a half-century later.

"[15]: 150 p. The series are mostly oil paintings on canvas, but also include examples of enamel on copper, original engravings, and even a relief model in Wedgwood clay.

Art historian H. W. Janson repeated it "On a visit to North Africa, he had seen a horse killed by a lion; this experience haunted his imagination, and from it he developed a new type of animal picture full of Romantic feeling for the grandeur and violence of nature.

"[13]: 567 p.  However, research published in 1965 produced a rather persuasive argument that Stubbs in fact never traveled to Africa, and the actual inspiration for the painting was an antique sculpture he had seen in a well documented 1754 stay in Rome.

[16] Basil Taylor was commissioned in 1955 by Pelican Press to write the book Animal Painting in England – From Barlow to Landseer, which included a large segment on Stubbs.

[19] The record price for a Stubbs painting was set by the sale at auction of Gimcrack on Newmarket Heath, with a Trainer, a Stable-Lad, and a Jockey (1765) at Christie's in London in July 2011 for £22.4 million.

[23] The Tate Britain, in conjunction with the Yale Center for British Art, organized the largest exhibition ever devoted to Stubbs (up to that time) in 1984, which travelled to New Haven in 1985.