Siganus randalli was first formally described in 1990 by the ichthyologist David J. Woodland with the type locality given as a coral reef flat off Paruru Plantation in the Marau Lagoon on Guadalcanal Island in the Solomon Islands. The specific name honours the American ichthyologist John E. Randall of the Bishop Museum in Honolulu, Randall brought this species to Woodland's attention and gave him a lot of help with his revision of the genus Siganus.
