Gasteria pillansii is endemic to the dry winter rainfall region in a 100-150 km belt parallel to the west coast from just south of Clanwilliam, South Africa, to just north of the Orange River in southern Namibia, occurring in Succulent Karoo vegetation. It is found at elevations from close to sea level to about 1 000 m on the Namaqualand escarpment, mainly confined to the cooler southern and eastern aspects, underneath shrubs or shrublets or in the shade of rocks, rarely in exposed or north-facing aspects.

There is a distribution gap on the Knersvlakte between Vanrhynsdorp and Nuwerus. The rainfall, occurring from April to September, ranges from 25-200 mm per annum. Heavy fog from the Benguella Current (Atlantic Ocean) provides additional moisture. Light frost may occur in the area. Summers are very hot with temperatures often reaching 40º C. It grows on various rock and soil formations, but more commonly on sandstone, granite and shale. The soils are sandy and well drained with a pH of between 6.2 and 7.8.

Populations south of Clanwilliam occur on flat, rocky, sandstone ridges in the shade of Diospyros ramulosa and Montinia caryophyllacea. Other commonly associated succulent species in the habitat include Ruschia rariflora, Lampranthus thermarum, Tylecodon paniculatus, T. reticulatus, Cotyledon orbiculata, Prenia pallens and Stapelia hirsuta.

There is a marked vegetative resemblance to Gasteria disticha of the southern Great Karoo and Breede River Valley, which has similar leaves but G. disticha has smaller flowers of only 12-20 mm in length and the base of the flowers is markedly swollen (gasteriform) for about two-thirds of its length. In floral characters G. pillansii may be confused with G. acinacifolia, G. croucheri and G. batesiana from the eastern Lowveld regions of South Africa, but they are quite different, having leaves that are keeled and are arranged in a rosette. These species have a somewhat similar large perianth but G. pillansii differs from them in that its perianth has a swollen basal part for less than a third of its length.

Gasteria pillansii is very variable especially in leaf and perianth size. Towards the coast, near the Olifants River Mouth, the leaves become more markedly rough and covered with sand and dust. This variation is continuous and the small forms (leaves smaller than 70 mm) have been named G. pillansii var. ernesti-ruschii , which occurs near the Port Nolloth coast to southern Namibia.

Plants from the Oograbies Mountains in the Port Nolloth District occur on steep, rocky, southern and eastern aspects in quartzitic rock crevices. Associated plants in the habitat include Tylecodon racemosus, T. similis, T. schaeferianus, Haworthia arachnoidea, Conophytum stephanii, Crassula hemisphaerica, C. columella and various other succulent and geophytic species. A rich succulent flora probably the richest in the world, predominates in the these mountains.