Harrington Mann established his reputation as a portrait painter of international fame, though he also painted landscapes, marine and historical subjects. His success and clientele in the United States was significant enough for him to maintain a house in New York as well as his native Britain. The son of a chartered accountant, Mann had an equally international education studying first at the Glasgow School of Art and continuing at The Slade School of Art in London from 1880 under the direction of Alphonse Legros (1837-1911). While a student at the Slade, Mann won an Travelling Scholarship which he spent in Italy from 1887-89, after which he visited Algiers, Tangier and Spain before further studies in Paris as the pupil of Gustave Boulanger (1824-1888) and Jules Joseph Lefevre at the Académie Julian. Mann returned to Glasgow and worked as a designer for JW Guthrie (now Guthrie and Wells) during the 1890s, producing designs for stained glass windows at Trinity Church, Claremont Street in 1893. He also designed murals on the theme of Scottish Song for the Ewing Gilmour Institute for Girls at Alexandria in the Vale of Leven, Dunbartonshire, which housed the workers at the Turkey Red Dye Factory (c. 1888). Mann also drew illustrations for The Daily Graphic and The Scottish Art Review. The subject matter of his paintings at this time ranged from Yorkshire fisherman to large historical scenes such as The attack of the MacDonalds at Killiecrankie, 1689.
While associated with The Glasgow Boys in the 1880s (he was certainly good friends with John Lavery, whose portrait and that of his daughter Alice he painted), Mann was on the periphery rather than a full member. He was, however, a member of The Society of Eight.
In 1900, Harrington moved from Glasgow to London and began to concentrate on fashionable society portraits, including members of the Royal Family. He particularly excelled at painting children’s portraits. Having spent several profitable seasons in America, Mann began to divide his time between London and New York, setting up a second studio there in 1910. As well as writing an unpublished autobiography, Mann wrote a comprehensive guide to The Technique of Portrait Painting which was published in 1933.
Harrington Mann exhibited at many venues throughout his successful career (including International exhibitions in Munich), making his début at London’s Royal Academy in 1885. He also showed his work at the International Society from 1898 onwards. He was a member of numerous artistic societies including the Royal Society of Portrait Painters, the Royal Society of Painters and Etchers, the International Society and the New English Art Club.
The work of Harrington Mann is represented in the Dick Institute, East Ayrshire; University of Birmingham; Russell-Cotes Art Gallery & Museum, Bournemouth; Dundee Art Galleries and Museums; Scottish National Portrait Gallery, Edinburgh, City of Edinburgh Council; Kirkcaldy Galleries, Fife; Kelvingrove Art Gallery and Museum, Glasgow Museums Resource Centre, Glasgow, Hunterian Art Gallery, University of Glasgow; Imperial War Museums, National Portrait Gallery, Parliamentary Art Collection, Royal Academy of Arts and Tate Britain, London; National Trust for Scotland; Newcastle University; Nottingham Castle Museum and Art Gallery; Paisley Museum and Art Galleries, Renfrewshire; Ulster Museum, National Museums Northern Ireland; Pannett Art Gallery, Whitby and the Art Gallery of New South Wales, Sydney, Australia.
 Where he shared the studio of David Gauld in the early 1890s.
 Formed in Edinburgh in 1912, the Society of Eight included P.W. Adam, David Alison, F.C.B. Cadell, James Cadenhead, James Paterson, John Sinclair and Sir John Lavery as well as Harrington Mann. William Hardie describes them as a group of ‘united artists who all tended to adopt a painterly approach and to use a light-keyed colour.’ W Hardie, Scottish Painting 1837-1939, Studio Vista, London, p. 100.