Leopold Kessler, German mining engineer and Zionist, was the son of Jacob Kessler and his wife Johanna Feig. He studied at the mining academy in Freiberg, then for a year at the Royal School of Mines in Berlin, and returned to Freiberg to complete his studies. His experiences of anti-Semitism led him to leave Germany. After working for some time as a mining engineer in Rhodesia (now Zimbabwe) he settled in Johannesburg in 1893 and took part in the development of Crown Mines and the Kleinfontein gold mine.
In June 1894 he requested a patent for a new method to make bricks from mine tailings and mud. That same year he became a member of the newly established Chemical and Metallurgical Society of South Africa (from 1902 the Chemical, Metallurgical and Mining Society of South Africa). He was still a member in 1905, when he was listed as a consulting mining engineer and metallurgist, but of unknown address. He was an early member also of the Geological Society of South Africa (founded in 1895) and of the South African Association for the Advancement of Science (founded in 1902). In 1902 he published his Valuation plan of the Witwatersrand goldfields (London, 1902), followed two years later by The gold mines of the Witwatersrand and the determination of their value (London, 1904, 135 pp).
Kessler became a naturalized British citizen of the Transvaal Colony in 1905. He was one of the first South African Zionists and a friend of Dr Theodor Herzl, founder of the movement for the return of the Jews to Palestine. In 1900 he was one of the three representatives of Dorshei Zion (a local Zionist society) to the Fourth Zionist Congress. In 1901 he visited Uganda, proposed by the British Colonial Office as an alternative for Jewish settlement, and in 1903 was president of the Transvaal Zionist Association. He continued to represent South Africa at international Zionist meetings for many years and in 1918 delivered a lecture in London on the history and development of Jewish colonisation in Palestine. His musical talents found expression in the composition of a piano solo, "McKinley and Hobart march...", published in Boston in 1896.
Kessler's last known address in South Africa is Rayton, Transvaal - a town established in 1903 some 40 km east of Pretoria by the Montrose Diamond Mining Company. He left South Africa around 1906 and during his subsequent career was involved in mining in Morocco, the United States, and Cuba. However, he returned to South Africa later, for in 1916 he was accused here by C. Mulnersi of making disloyal remarks during World War I (1914-1918). He was married to Annette Grace Kessler, with whom he had three children.