Four novel dinuclear phosphanegold(I) complexes containing bis(diphenylphosphano)alkanes and (biphenyl-2-yl)di-tert-butylphosphane (Bdbp), Au2(Bdbp)2(Dppe)2 (1), Au2(Bdbp)2(Dppp)2 (2), Au2(Bdbp)2(Dppb)2 (3) and Au2(Bdbp)2(Dpma)2 (4) (where Dppe = 1,2-bis(diphenylphosphano)ethane, Dppp = 1,3-bis(diphenylphosphano)propane, Dppb = 1,4-bis(diphenylphosphano)butane and Dpma = bis[2-(diphenylphosphano)methyl]amine), were synthesized and characterized by elemental analysis, FTIR and NMR spectroscopies. The structures of three of the complexes (1, 2 and 4) were determined by X-ray crystallography, which reveals that the complexes exist as dinuclear species, in which the gold(I) atom is linearly coordinated to the phosphorus (P2) and (P1) atoms. The in vitro cytotoxicity of the complexes was investigated against two established human cancer cell models, colorectal (HCT-116) and breast (MCF7) cancer cells. All four complexes showed excellent cytotoxicity against both cell models with significantly lower IC50 values than that of cisplatin. The mitochondrial membrane potential (ΔΨm) was also assessed to get a better understanding of the underlying molecular mechanism of toxicity. The exposure of the complexes for 24 hours resulted in mitochondrial depolarization (reduced mitochondrial health) thereby potentially triggering the release of cytochrome c and apoptotic cell death. Together, the findings of our studies demonstrate that the novel gold(I) complexes have superior anticancer activity compared to conventional cisplatin, which is potentially mediated through the disruption of ΔΨm and induction of apoptosis.