Lampranthus roseus is a perennial mesemb growing into a mat or low dome-shaped mound. The branched stems spread, their tips erect. The succulent leaves are grey-green, narrow and triangular in shape. They are opposite, the pairs often slightly curving in towards each other.

The flowers of L. roseus are brightly showy as the generic name indicates (lampros meaning bright, anthos meaning flower, both words are Greek). In season, the shrublet may be so covered in flowers that the leaves are invisible, taking a break from their photosynthetic duties. The pink-purple flowers have shiny petals with pale yellow centres.

Flowering happens in spring and summer. The woody capsules are funnel-shaped with five locules (Smith, et al, 1988).