Baeckea leptocaulis is a shrub that typically grows to a height of and has grey or brownbranchlets. The leaves are linear, mostly long and wide on a petiole long. The flowers are about in diameter and are borne in leaf axils on a peduncle about long, each flower on a pedicel long. The sepals are oblong, about long and the petals are white, more or less round and long. There are five or six stamens, the ovary has two locules and the style is about long. Flowering occurs between December and March and the fruit is a cylindrical to bell-shaped capsule long and wide.