Baeckea trapeza is a shrub that typically grows to a height of up to and has grey, scaly bark. The leaves are lance-shaped with the narrower end towards the base, long and long on a petiole about long. The flowers are up to wide on a pedicel long with linear bracteoles long but that fall as the flowers open. The five sepals are long and more or less round and the petals are long. There are eight to eleven stamens opposite the sepals and the style is about long. Flowering has been observed in January and April and the fruit is conical to bell-shapedcapsule in long and wide.