Clemens Mayer, described as colonial viticulturalist in the Department of Agriculture of the Cape Colony, published an article on "The planting of new vineyards" in the Agricultural Journal of the Cape of Good Hope (Vol. 1, pp. 65-66) in 1888, and contributed some other brief items to the same volume.
In November 1890 he was appointed phylloxera officer in the Viticultural Branch of the Department of Agriculture. On 1 July 1893 he became an agricultural assistant in the same department and two years later visited Europe to buy apparatus for wine making. He published an article on "The reconstitution and future cultivation of vineyards" in the Agricultural Journal of the Cape of Good Hope in 1897 (Vol. 11(3), pp. 118-123). By 1898 he was stationed at Stellenbosch. His annual report for 1899 dealt mainly with vines and the phylloxera problem, though he also gave attention to fruit culture in general. He, with P.J. Cillie* and C.G. Marais, wrote a brief Report on the failure of hanepoot grafts on American vines which was published as Pamphlet No. 16, 1899, of the Department of Agriculture. At this time he also lectured at the Elsenburg Agricultural College near Stellenbosch. Two years later he published The making of wine and its bye-products, brandy, and vinegar... (Cape Town, 1901). From September 1904 he was for a short time acting viticulturalist at Elsenburg, but appears to have retired on pension soon afterwards. In 1909 he published an article on correct and profitable manuring, "Nitrate of soda or sulphate of ammonia?" in the Agricultural Journal of the Cape of Good Hope (Vol. 35(1), pp. 24-27.
Mayer became a member of the South African Philosophical Society in 1896, but ended his membership at some time between 1900 and 1906. He was interned in South Africa during World War I (1914-1918).