Rhizanthella johnstonii is a leafless, sympodial, subterranean herb with a horizontal rhizome below the soil surface with an erect peduncle up to long. Up to sixty small, white flowers tinged with pink are arranged in eight to twelve spiral rows, each with six to eight flowers wide, surrounded by six to eight cream-coloured to pale pinkish cream bracts. In other respects, it is similar to R. gardneri.
