Jamesbrittenia maxii is a shrublet that branches and spreads from a woody base. The leaves are broadly ovate with rounded or pointed tips and serrated margins. The dark green leaf surfaces have prominent veins on the lower surface; are sunken above.
The flower of J. maxii has five widely spreading white corolla lobes. The slender cylindrical corolla tube with olive green colouring inside the throat has a bend near the flower mouth. Fine dark lines continue from inside the throat for a short distance onto the lobes. The yellow anthers visible in the flower mouth are not exserted.
The distribution of this plant lies in the Richtersveld and Namaqualand in the Northern Cape, but more widely over the border in Namibia. Early in the 21st century the plant population is stable enough not to cause concern over its future in nature (JSTOR; iSpot; www.redlist.sanbi.org).