Individuals within this species produce a short rhizome giving it a tufted, rigidly erect appearance. When growing as a colony this can appear as a spreading growth habit also. Leaves are slender and similar in appearance to the flower-stems (culms) with the tallest culms longer than the leaves.
Leaves are generally biconvex, smooth with red-brown sheaths at their base.
New narrow red-brown spikelets appear in spring with small pale brown nuts produced in summer. Often the seedheads fail to produce viable seed. Older culms are retained on the plant becoming grey with age.
There a number of Lepidosperma species on our coast and in the Surf Coast. Slender Sword-sedge used to be considered as part of the 'Variable Sword-sedge' (Lepidosperma laterale) group which grows nearby. It is found along the clifftops of Jan Juc in transitional grassland/coastal scrub. It prefers moist sites.