The structure and chemical bonding in the Re₃O₃⁻ cluster are investigated using photoelectron spectroscopy and density-functional theory calculations. Vibrationally-resolved photoelectron spectra were obtained, yielding an accurate electron affinity (2.54 ± 0.02 eV) and a ground-state ReO stretching frequency (960 ± 30 cm⁻¹) for the Re₃O₃ neutral cluster. It is shown that the Re₃O₃⁻ cluster possesses a C_2v (¹A₁) ground-state structure consisting of a Re₃ triangle with one bridging and two terminal oxygens. Molecular orbital analysis reveals that the Re₃ core in Re₃O₃⁻ possesses conflicting d-orbital aromaticity (π-antiaromatic and σ-aromatic), consistent with its C_2v symmetry. Well-resolved photodetachment transitions from the Re 5d_z² δ orbitals allow the bond strength and resonance energy of a delocalized δ-bond to be estimated.