Gerhard Mari Johan van Dam was born on 9 October 1855at Delfshaven, Nederland. and moved with his parents to the Transvaal in 1868.
When President Pretorius was taken prisoner by the British in January 1880 van Dam was present and was a commando formed at Nauwpoort near Potchefstroom and was he chosen with General Koch to investigate the incident.
In November 1880 he was with the Schoonspruit commando that defend Cronje, Besuidenhout and others .
He was appointed to secretary of the Volks Committee and at the meeting at Paardekraal on 12 December he was chosen as Secretary of the Volksraad.
He was part of the commando under General Cronje that went to Natal.
In September 1888 he was appointed as Commandant of police at the Klerksdorp goldfields and was then transferred to Johannesburg as second in command.
In November 1896 he was appointed as Commandant of Police of the Witwaterrand Goldfields and had that position when the war broke out.
On 19 April 1901 he and two other men was captured by the British and Swazi warriors at a kraal. Sergant Major Lombaard was killed and Van Dam was wounded.
He was caught and sent to Durban and from there to Cape Town and later to the prisoner camp near Ladysmith till the end of the war.