Shortly after he was born his parents left Australia for Kirkcudbright in Scotland, where he remained for most of his life. He studied for three years at Edinburgh College of Art, and for two years at the Royal Academy of Fine Arts in Antwerp under Professor Verlat. Returning to Scotland in 1885, he met George Henry and associated himself with the Glasgow Boys.
Hornel and Henry collaborated on many projects and in the early 1890’s the two artists spent a year and a half in Japan, where Hornel learned much about decorative design and spacing. Towards the close of the decade, his colours preserving their glow and richness, became more refined and more atmospheric, and his drawing more naturalistic, combining sensuous appeal with emotional and poetic significance. In 1901 he declined election to the Royal Scottish Academy. A member of Glasgow Art Club, Hornel exhibited in the club’s annual exhibitions.
In 1901 he acquired Broughton House, a townhouse and garden in Kirkcudbright, which was his main residence for the rest of his life with his sister Elizabeth. There he made several modifications to the house and designed garden taking inspiration from his travels in Japan. he also made an addition of a gallery for his paintings. On his death the house and library were donated and Broughton House is now administered by the National Trust for Scotland.