John Duthie entered the civil service of the Cape Colony on 1 October 1867. By 1879 he was the lighthouse keeper at Cape St Francis, and that year the Meteorological Commission of the Cape of Good Hope supplied him with a barometer, wet and dry bulb thermometer, anemometer, and rain gauge. He supplied regular meteorological observations from the beginning of 1880, summaries of which were published in the Commission's annual Report. On 7 September 1883 he was transferred to Port Elizabeth as lighthouse keeper. There he continued his meteorological observations until the end of 1899, a total period of 20 years, at the end of which he left the civil service.