Tyrannomyrmex legatus is a tropical Old World species of ants in the subfamily Myrmicinae.

[1] This single specimen was collected from leaf litter in lowland dipterocarp forest in southern Sri Lanka, near a stream at the bottom of a slope in the drier period of the year.

[1][2] T. legatus is most easily distinguished from T. rex and T. dux by differences in pilosity, sculpture and the shape of the petiole and postpetiole.

T. rex is almost lacking pilosity on the mesosomal dorsum, while the whole dorsal surface is covered with long erect hairs in T. legatus and T. dux.

In lateral view, the peduncle of the petiole is not clearly differentiated, with an abrupt anterior slope of the node.