Harold Scott Harger, son of Lieutenant-Colonel John Harger, was educated in England at Bedford and Devon County Schools. He came to the Transvaal in 1889 as a young man of 19 and in 1896 married the widow Selina G. Brown. He settled in Johannesburg for the rest of his life, practising as a consulting geologist and mining engineer from 1905. Geology, and particularly the formation of diamonds, was his main interest and by 1908 he claimed to possess the finest collection of rocks and minerals from South African diamond pipes and fissures in the world. His geological discoveries included the diamond deposits that gave rise to the Voorspoed Diamond Mine, and the Lion Hill Mine. For a number of years he prospected in the western Transvaal (now North-West Province), where he found alluvial diamond deposits on which several of the Lichtenburg diggings were proclaimed. As a result of these discoveries he was considered a leading authority on alluvial diamonds.
Being a master of both the written and spoken word Harger presented numerous geological and mining papers, and during 1897 and 1898 was the mining editor of the journal Machinery. His first paper, "Origin of diamonds: Criticism of Professor Jules Garnier's* paper", published in the Transactions of the Geological Society of South Africa (1897, Vol. 2, pp. 124-127) was the first of many over a period of some 40 years dealing with the origin and discoveries of diamonds and the minerals of Kimberlite. One of the most important of his papers was "The diamond mines and fissures of South Africa", which he read in Johannesburg before the joint meeting of the British and South African Associations for the Advancement of Science on 1 September 1905. It was published in the meeting's Adresses and papers... (Vol. 2, pp. 132-143), as well as in the Transactions of the Geological Society of South Africa. Another of his early achievements was to be the first to record the reddish sandstone with conglomerates that occurs between Pretoria and Middelburg. The find was reported in the Transactions (Vol. 3, pp. 107-108) in 1898, and the next year the strata were named the Waterberg sandstone formation by G.A.F. Molengraaff*. On a different topic he published "The underground erosion of the south-western Transvaal dolomites" (South African Geographical Journal, 1922, Vol. 5, pp. 55-65). Later in life he wrote some historical papers: "An early Transvaal geological map by Carl Mauch*" (1934); two contributions on the history of the Geological Society of South Africa (1939, 1945); and "Historical notes on the Geological Museum of Johannesburg" (1942).
In the course of his professional life Harger assembled an extensive collection of stone artefacts, probably mainly while prospecting for alluvial diamonds. In 1934 he donated the entire collection to the City Council of Johannesburg. It became known as the Harold Harger Archaeological Collection and was administered as a separate collection by the Johannesburg Geological Museum.
Harger was a Fellow of the Geological Society of London. In 1895 he became a foundation member of the Geological Society of South Africa and served on its council from 1897 to his death - an unprecedented term of more that 50 years. In 1912 he was the society's president, delivering his presidential address on "Some features associated with the denudation of the South African continent" (Proceedings of the Geological Society of South Africa, 1913, Vol. 16, pp. 22-39). Throughout his career he was one of the society's highly respected and leading members. He joined the South African Philosophical Society in 1905 and remained a member of its successor, the Royal Society of South Africa. He was also a member of the South African Association for the Advancement of Science. From 1913 to his death in 1947 he served on the Johannesburg Library Committee. During World War I (1914-1918) he served with the Mounted Maxim Guns in South West Africa (now Namibia). In 1935 he became a member of a consultative committee formed to advise on and assist in the development of the Johannesburg Geological Museum, remaining a member to his death. In recognition of his valuable services to the earth sciences in South Africa the Geological Society of South Africa awarded him the Draper Memorial Medal, its highest scientific award, in 1940. His scrapbook on diamonds in South Africa and elsewhere is in the library of the University of the Witwatersrand.
Harger was married to Selina Georgina Peters. After her death in 1908 he married Kathleen Constance Gilchrist. He had one surviving daughter and was a South African citizen.