Walter Clarke Buchanan was born on 20 June 1838 at Auchenbreck in the parish of Kilmodan, Argyllshire, Scotland, the son of Donald McChananich, a farmer, and his wife, Janet Clarke. (He was baptised under his father's name, McChananich, the Gaelic version of Buchanan.) Walter was educated at the parish school of Glendaruel and at Greenock Academy. At the age of 18 he emigrated to Australia and spent six years as a stockman in Victoria.
After moving to Otago, New Zealand, about 1863, Buchanan and a partner, John Ferguson, found work carrying and stock-dealing on the Otago goldfields. In 1865 they moved to Canterbury and rented a farm, but the gold discoveries of that year lured them to the West Coast where they engaged in packing and ran a store in Hokitika. Two years later Buchanan returned to Canterbury and used a Halswell farm largely as a base for further stock trading.
About 1871 Buchanan shifted to the North Island. In 1873 he raised a £20,000 mortgage and bought the 10,000-acre Tūpurupuru run in south Wairarapa for £21,000. Buchanan cleared almost all the original bush and established an English Leicester flock, later specialising in Lincolns and in shorthorn cattle. He worked hard to improve his property, paying very careful attention to the marketing of the stock. Unlike some other station owners he was personally frugal and led a simple life without lavish expenditure on houses. He never married.
Buchanan took an active part in farmers' organisations. He was one of the founders of the Wairarapa and East Coast Pastoral and Agricultural Society in 1877 and served as its president. He played a leading role in campaigns to eradicate scab and rabbits. Buchanan also worked to bring down freight rates for farmers, and was instrumental in forming, in 1912, a farmers' shipping company, Geo. H. Scales Limited.
A tireless advocate of the frozen-meat trade, Buchanan was the principal promoter of the Wellington Meat Export Company; he chaired its first meeting on 6 September 1881, and served as its chairman for the next 12 years and as a member of the board for many years after that. He assisted in the establishment of several dairy factories and was the first chairman of directors of the co-operative dairy company formed at Greytown in 1881.
Buchanan inevitably entered national politics. He was MHR for Wairarapa South (1881–87), and then represented Wairarapa (1887–99, 1902–5, and 1908–14). J. T. M. Hornsby, a Liberal, whose support lay in small towns, defeated him in 1899, 1905 and 1914. Buchanan was a staunch conservative, supporting free trade in the 1880s and opposing Premier Harry Atkinson's protective tariff in 1888. He was a strong critic of the Liberal reforming legislation of the 1890s. Although entirely devoid of parliamentary eloquence, he was perceived as possessing a 'phenomenal capacity for…legislative drudgery.' He was described as being 'as blunt as the square toe of his boots', and 'one of a brace of the bitterest anti-Seddon politicians in either House'.
Buchanan's wealth gave him considerable influence in conservative politics, particularly in the years of opposition prior to 1912. In 1907 he bought 800 £5 shares at the founding of the Dominion as a newspaper supporting the opposition. Although he never attained ministerial office, behind the scenes he exercised much influence and became a close adviser to William Massey. He was knighted in 1912 and appointed to the Legislative Council in 1915.
A member of the Wellington Education Board for 34 years, Buchanan was especially interested in agricultural education. In 1923 he presented £10,000 to Victoria University College for the establishment of the Walter Clarke Buchanan chair of agriculture. It was transferred in 1926 to what was soon to become Massey Agricultural College.
Buchanan was a 'wiry, undistinguished man' with an untireable energy. He was of medium height with rugged and weather-scarred features; his 'perpetual frown' was 'topped off with the bushiest eyebrows ever seen in the House'. While he seemed shy, he was on closer acquaintance very genial and kind-hearted. He made numerous charitable donations, including, in 1909, £4,000 for the erection of the Buchanan Home for incurables at Greytown.
Buchanan's busy public life meant that much of the detailed management of Tupurupuru had had to be left to managers. Its value had increased to £53,000 by 1890. In 1905 Buchanan commenced a series of transfers to relatives. After the homestead was destroyed by fire in 1917, he moved to Masterton, where he died of heart failure after a car accident on 19 July 1924. The 4,974 acres which remained of Tūpurupuru after his death were partly subdivided by the Crown.
Walter Clarke Buchanan was a significant farmer-politician in an era when, as never before, the interests of farmers required effective political advocacy. He was instrumental, too, in helping to make farmers a dominant force in New Zealand politics.