[4][5] Sarel Oosthuizen was the eldest child of Voortrekker Daniel Jacobus Oosthuizen (Prince Albert, South Africa (Albertsburg), 26 July 1821 - Sterkfontein, Krugersdorp, 6 June 1899) and his second wife Anna Susanna du Toit (14 November 1840 - Krugersdorp, 20 September 1921), among in total five sons and three daughters of this couple.

[8] In 1899 Oosthuizen was elected field cornet (Afrikaans: veldkornet) for his town of Krugersdorp and left with this Commando for the Natal front against the British.

Later he joined in the Boer derailing of a British armoured reconnaissance train at Chieveley on 15 November 1899 and apprehended its passenger The Morning Post reporter Winston Churchill,[9] who later erroneously thought that he was arrested by Louis Botha.

[11] He distinguished himself in the Battle of Spion Kop (Slag van Spioenkop, 23–24 January 1900)[8] and was made a fighting general (Afrikaans: veggeneraal) on 24 February 1900.

[15] However, Oosthuizen died on 14 August 1900 of the wound in his thigh incurred at the Battle of Dwarsvlei near his farm on 11 July 1900, where he had tried in vain to capture the guns of Smith-Dorrien's men.