Drosera marchantii is an erect tuberous sundew from Jarrah woodland in Western Australia. The species is named in honour of Neville Marchant, a notable systematic botanist.

Drosera marchantii has an erect stem that usually grows around 30 cm tall. The stem is glabrous, with non-carnivorous bracts at the base. The leaves are orbicular and occur singly along the stem. Flowering typically occurs only after a bushfire in the preceding season. The flowers are pink with long, oval petals. In non-flowering specimens, the stem gets progressively smaller towards the terminus.

The species grows in jarrah forest, generally in leaf litter on laterite or sandy habitats on well-drained slopes. It is mainly distributed in the Darling Range adjacent to the swan coastal plain.

Drosera marchantii is most similar to Drosera prophylla. D. marchantii is distinguished by its fewer bracts at the base of the plant and more southerly distribution (D. marchantii has many bracts and is found in the laterite hills north of Perth). The species is also somewhat similar to D. huegelii but differs in that the laminae are shallowly pitted and dangle less (the laminae of D. huegelii are deeply pitted and hang downwards). It can be similar to immature plants of other erect sundews but is distinguishable by its glabrous stems and leaves that occur single (as opposed to sets of three).