Both brothers fought in the First Boer War (1880–1881) at the Battle of Majuba Hill and Piet de Wet participated in the expedition to capture Mampuru II.

De Wet represented Midden-Liebensbergvlei-wyk in the Volksraad from 1895 to 1897, moved to Pretoria, but came back and became military commander (veldkornet, field cornet) for Lindley.

[7] However, after the occupation by Roberts of Kroonstad on 12 May 1900,[8] Free State soldiers were disheartenend and Piet de Wet had started to doubt the use of fighting on.

[8] On 18 May 1900, British brigade general Robert Broadwood received a message that Piet de Wet was willing to surrender on the condition that he and his men could return to their farms.

[9] But in July 1900, Piet de Wet and several of his staff surrendered to the British at Kroonstad, becoming "joiners", "hensoppers" (hands-upper), and "wapenneerlêers" (who put down their weapons).