Sladenia gardineri was first formally described in 1908 by the English ichthyologist Charles Tate Regan with its type locality given as Salomon Atoll in the Chagos Archipelago of the Indian Ocean.

[3] The genus Sladenia is one of 4 extant genera in the family Lophiidae which the 5th edition of Fishes of the World classifies in the monotypic suborder Lophioidei within the order Lophiiformes.

The holotype of S. gardineri was collected during an expedition funded by his memorial trust.

The specific name gardineri honours John Stanley Gardiner, the British zoologist who collected the holotype.

[6] Sladenia gardineri is found in the Chagos Archipelago in the central Indian Ocean[7] and has been recorded in the western Pacific Ocean off New South Wales,[8] although these specimens may represent an undescribed species or S.