Louis I. Seymour, mechanical engineer, was the son of George W. Seymour and his wife Mary Freeman. He attended school at the Whitney Point academy, but did not go to university. After serving an apprenticeship in engineering he obtained further experience in various firms, including some in Scranton, Pennsylvania. Thereafter he spent two years installing machinery at the El Callao Mine in Venezuela. In June 1886 he married Catherine Perry, but they had no children.
Seymour was appointed mechanical engineer to De Beers Consolidated Mines in Kimberley about 1889, though he may have spent some of his time in England. In 1893 he became managing director of Fraser & Chalmers at Erith, on the outskirts of London, but in 1896 came to Johannesburg to take up the position of chief mechanical engineer to Rand Mines and other companies in the Eckstein group. In August 1896 he became a member of the South African Association of Engineers and Architects (which changed its name to the South African Association of Engineers in 1898). He was elected a member of the association's council for 1897-1898, as joint vice-president for 1898-1899, and as president for 1899-1900. In September 1897 he read a paper before the association on "Rock drilling: comparative results" and in May 1898 another on "Tests of a King-Riedler air compressor". Both were published in the Proceedings (1897-1898, Vol. 4, pp. 45-52 and 169-175). Meanwhile he had participated in founding the Mechanical Engineers' Association of the Witwatersrand in May 1898 and was elected its honorary president (the president was W.H. Wood*). He was an examiner in engineering for the final mining examination of the University of the Cape of Good Hope in 1898.
When the Anglo-Boer War (1899-1902) broke out in October 1899 Seymour went to Cape Town and took a leading role in raising the Cape Railway Pioneer Regiment, an engineering corps consisting mainly of technical staff from the Witwatersrand. He was the regiment's second-in-command, with the rank of major, and was responsible for valuable military engineering. However, after only a few months he was killed when working on a bridge at the Sand River, near Virginia.
Seymour was greatly esteemed, both as a person and as an engineer, and was probably the most prominent mechanical engineer in South Africa in his time. Soon after his death his colleagues in the Mechanical Engineer's Association of the Witwatersrand established a fund which was used to commission an oil painting of him. Another fund was established to found the Seymour Memorial Library, which was opened in 1905. It developed into the principal technical library in the country and from 1927 was administered by the Johannesburg Public Library.