Harold Clarkson Fletcher, son of Robert Fleming and his wife Fanny, was educated at the King Edward School, Birmingham, served an apprenticeship with Messrs Belliss & Morcom of that city, and qualified as a Member of the Institution of Mechanical Engineers. He came to South Africa in 1892 and acted as consulting mechanical engineer to a number of Rand gold mining companies. In July 1896 he delivered a paper on "Bottom discharges from cyanide vats" before the Chemical and Metallurgical Society of South Africa (though he was not a member at that time); the paper was published in the society's Proceedings (Vol. 1, pp. 244-247).
In 1897 Fletcher entered into a partnership with George Johnson. They opened a consulting and general engineering business in Southern Rhodesia (now Zimbabwe) that year, under the name Johnson & Fletcher, with branches in Bulawayo, Salisbury (now Harare) and Beira, Mozambique. Fletcher appears to have managed the Bulawayo office, for he represented the firm in that city for the rest of his career. By 1944 he was Managing Director of the firm.
He became a member of the South African Association of Engineers and Architects in January 1898 and in 1944 still belonged to its successor, the South African Institution of Engineers. In 1901 he joined the Rhodesia Scientific Association, established in Bulawayo in 1899, and was still a member in 1931. In 1940 he was a corresponding member of the council of the Chemical, Metallurgical and Mining Society of South Africa.
In his later years Fletcher was attracted to spiritualism and published Psychic episodes of great Zimbabwe, a true narrative... through the trance mediumship of Richard E. Pugh (Cape Town, 1941), a 100 page book complete with illustrations, plates, map and plans. He was survived by his wife Maud Hilda Emma Fletcher, born Child.