This species probably lived near a freshwater lake, and probably hunted for other small creatures that lived in the same habitat. It was a slender animal, with rather small legs and a long tail. Together with Casineria, another transitional fossil found in Scotland, it is one of the smallest reptile-like amphibians known, being a mere 20 cm in adult length. The small size has made it a key fossil in the search for the earliest amniote, as amniote eggs are thought to have evolved in very small animals. Advanced features that tie it in with the reptilian rather than amphibian group include unfused ankle bones, lack of labyrinthodont infolding of the dentin, the lack of an otic notch, and a generally small skull.
Ruta & al. (2003) interpreted the long body and small legs as a possible adaption to burrowing, similar to that seen in modern skinks.
The phylogenetic placement of Westlothiana has varied from basal amniote (i.e. a primitive reptile) to a basal Lepospondyl, in an analysis with the lepospondyls branching of from within Reptiliomorpha. The actual phyllogenetic position of Westlothiana is uncertain, reflecting both the fragmentary nature of the find and the uncertainty of labyrinthodont phylogeny in general.