Reverend Charles Daniel Helm was the son of Reverend Daniel Helm, a missionary of the London Missionary Society at Zuurbraak (now Suurbraak) just east of Swellendam. Charles Helm - presumably him - studied at the South African College from 1866 to 1868. In the latter year he went to London, where he continued his studies at New College, London, until 1873 and qualified as a Protestant missionary. That same year he married Baroness Elizabeth von Puttkamer. Still in 1873 he joined the London Missionary Society, returned to the Cape, and was stationed at Zuurbraak. In October the next year he started out for Matabeleland, in what is now Zimbabwe, finally arriving at Hope Fountain, at present Bulawayo, in December 1875. He moved around for some time owing to his wife's health problems, but in 1876 took over the mission station from Reverend J.B. Thompson. During June-July 1878 the hunter-explorer F.C. Selous* stayed with him there. By 1880 he was postmaster for Bulawayo. Two years later he urgently requested the London Missionary Society to send him a new set of dental instruments, as his ability to extract teeth was much in demand. He probably visited England from 1886, but was back in Bulawayo by May 1888 and remained there until his death. During the late nineteen-eighties he became a trusted confidant of King Lobengula. He was the co-translator (with W.A. Elliott) of a New Testament and Psalms into Ndebele in 1903 and retired shortly before his death.
Helm undertook regular meteorological observations at a second order meteorological station at Hope Fountain, equipped by the Cape of Good Hope Meteorological Commission. He reported his results to the Commission from 1899 to 1901, and again from 1904 to 1908, for inclusion in its annual reports. The results were also made available to the Rhodesia Scientific Association, of which he was a member. In September 1901 a paper based mainly on his rainfall data, "Climatic observations at Hope Fountain", was read before the Association by Henry Wallis and published in the Proceedings (Vol. 2, pp. 65-73). At the annual general meeting of the Association in June 1905 Helm was thanked by Council for his valuable meteorological observations.