Daniel Petrus Marais joined the Pretoria Commando under General Schoeman on 25 October 1899. He participated in the following skirmishes or battles: 30 October 1899 near Colesberg under General Schoeman; Sandrivier, Oranje Vrijstaat under General Bouwer; Kliprivier near Klerksdorp under General Erasmus; Slag van Donkerhoek, 11-12 June 1900 under General Liebenberg; Slag van Frederikstad near Potchefstroom, 20-25 September 1900 under General Liebenberg.
Veldkornet Daniel Petrus Marais was wounded in both shoulders and an arm, and captured on 25 September 1900 at Frederikstad. He was treated by a British doctor and taken as a POW to St. Helena where he stayed until after the armistice.
Marais died on 26 January 1928. He is buried in the Old Cemetery, Lady Grey, Eastern Cape, South Africa. According to the Death Register, he was 53 years old when he died. The Death Register comments as follows: "Deur Blits getref op straat. Hy was stokdoof en laat na vrou en hinders."