John Isidore Hoffmann studied at Owens College, Manchester, and in Vienna, Austria. After serving an apprenticeship at Nasmyth, Wilson & Co. in Manchester he moved to South America where he served in the Argentine Navy for a short period and was then engaged on harbour, river and railway surveys in Paraguay, Argentina and Uruguay for five years. He first came to the Transvaal in 1891, and three years later married Ada Brown of Southport; they eventually had two children. In 1898 he went to Mexico, but returned to South Africa in 1901. He settled in Johannesburg as a consulting mining engineer in 1902, after the Anglo-Boer War (1899-1902). He became an associate member of the Institution of Civil Engineers (London) in 1894 and was a member of both the American Institute of Mining Engineers and the (British) Institution of Mining and Metallurgy.
In 1906 John Isidore Hoffmann and his partner, Alick J. Lambert, were declared insolvent. In 1908 (but not thereafter) J.I. Hoffmann was listed as a consulting engineer in Fox Street, Johannesburg. That same year he was co-author (with E.J.P. Jorissen*) of a Report on the tin deposits of the farm Zwartkloof... in the Waterberg. The report included a geological sketch map of the farm, signed by J.I. Hofffman, consulting engineer, and E. Jorissen. In 1910 Hoffmann applied for permission to prospect on government land near Potchefstroom.
At the time of his death Hoffmann was the director and engineer of mining undertakings in Serbia and the Sudan.