<p>Delocalized [4<i>n</i> + 2]π-aromaticity in cyclic planar unsaturated organic molecules conceptually underpins organic chemistry. Recently, the study of all-metal aromaticity has burgeoned, but although there has been interest in cyclo-{E₃} (E = P, As, Sb, Bi) species as cyclopropenium analogues, the formation of cyclo-{Bi₃} remains rare. Thus, the potential aromaticity of 2/6π-cyclo-Bi₃^+/3−, as the heaviest 6<i>p</i> analogue of cyclopropylium, has remained open to different interpretations. Here we report the formation of diuranium and dithorium 6π-cyclo-Bi₃³⁻ inverse sandwich complexes, complementing the small number of acyclic- and cyclic-Bi_<i>n</i> (<i>n</i> = 3–5) compounds. The 6π-cyclo-Bi₃³⁻ ring exhibits substantial ring currents, similar to 6π-benzene, 2π-(C₃H₃)⁺ or 6π-(C₃H₃)³⁻. Calculations reveal similar ring currents for 6π-cyclo-Bi₃³⁻, 2π-cyclo-Bi₃⁺ and 0π-cyclo-Bi₃³⁺, demonstrating σ-aromaticity that is dominant over π-aromaticity in cyclo-Bi₃³⁻, despite the favourability of describing cyclo-Bi₃³⁻ with localized rather than delocalized bond descriptions. Confirmation of 6π-cyclo-Bi₃³⁻ σ-aromaticity provides the heaviest all-metal 6<i>p</i> analogue to π-aromatic (C₃H₃)^+/3−, leading to organic–inorganic aromaticity benchmarking.</p><p></p>