In this article, we report IriPlatins 1-3, a new class of heterobimetallic Ir(III)-Pt(IV) conjugates as multifunctional potent anticancer theranostic agents. In the designed construction, the octahedral Pt(IV) prodrug is tethered to the cancer cell targeting biotin ligand through one of the axial sites and the other axial site of Pt(IV) center is attached to multifunctional Ir(III) complexes that possess organelle-targeting capabilities with excellent anticancer and imaging properties. The conjugates preferentially accumulate within the mitochondria of cancer cells, and subsequently, Pt(IV) is reduced to Pt(II) species that concomitantly releases both the Ir(III) complex and biotin from its axial sites. The IriPlatin conjugates demonstrate potent anticancer activity in various 2D monolayer cancer cells, including the cisplatin-resistant cells in the nanomolar concentrations and 3D multicellular tumor spheroids. The mechanistic investigation of conjugates suggests that the loss of MMP, generation of ROS, and caspase-3-mediated apoptosis are responsible for cell death.