Maritz qualified for the Middle Temple in November 1912 and began practising as an advocate in Pretoria I 1913. During the Rebellion of 1914, he sympathised with the rebels and in an effort to join the rebel armed forces, he was arrested and imprisoned at Nylstroom and later in Pretoria. After the rebellion ended and Maritz was set free, he was not welcomed back by the Pretoria Bar. As a result, Maritz, along with Tielman Roos and Oswald Pirow, formed an alternative Bar, the so-called "Rebel-Bar".