He was born in Australia, the son of Scottish immigrants. The family, however, returned to Kirkcudbright where Hornel grew up and settled. He trained at the Trustees Academy in Edinburgh and worked for a time in Belgium. Hornel met George Henry, with whom he shared a studio and collaborated on work such as The Druids Bringing Home the Mistletoe (1890). The pair travelled to Japan, a trip which had a great influence on Hornel, who went on to produce a series of paintings of Japan. Hornel became an early member of the influential group of painters known as the "Glasgow Boys," which included Henry, James Guthrie, E.A. Walton, and John Lavery.
From the Scottish National Tourist Board:
His later work lacked the vitality of his Japanese paintings, becoming increasingly formulaic, as epitomised by his popular scenes of young children playing amongst flowers which he reworked in numerous variations. It is for these later works that he is still chiefly remembered while the early work which placed him at the very forefront of progressive painting in Scotland and did much to earn Scottish art international acclaim, is now largely forgotten.
Lotus Flower, Japan
Druids, Bringing in the Mistletoe (1890--with George Henry)
Girls Gathering Flowers By the Seashore