Gasteria excelsa is one of the largest of the Gasteria species, second only to Gasteria acinacifolia in height. Plants can grow quite large and consist of numerous thick, robust, angled, leaves that are arranged in strong solitary basal rosettes, 30-60 cm tall and 60-75 cm wide. These are dark green, and mottled with faint white flecks. The leaves of fully grown plants are often channeled on the upper side, with sharp edges, and (like its relatives) a keel on their lower side. Inflorescences can grow very large and consist of many horizontal branches. Flowers are pink at the base and green at the tip.