Recent years have witnessed a growing interest in multicomponent reactions (MCRs) as environmental benign and reliable synthetic strategies for drug discovery. Though MCRs have been significantly explored in photoredox-transition metal dual catalysis, photocatalyst-copper dual catalysis is quite underdeveloped due to an unclear mechanistic basis. Herein, we discuss theoretical investigations unraveling the mechanistic avenues in IrIII-CuII dual catalyzed MCRs of a carboxylic acid (as an alkyl radical precursor X•), [1.1.1]propellane and a N-nucleophile leading to three component C–N coupled products, experimentally reported by MacMillan. We investigated the radical formation pathway, defined the favored photoredox catalytic cycle, and found the favorable reaction pathway within the Cu-catalytic cycle, and finally we elucidated the origin of selectivity between three-component and two-component coupling products. Our computations suggest that the N–H bond activation is the rate-limiting step. The preference for a two-component coupling product over a three-component product is governed by the relative stabilities of the CuII-X• intermediates. Energy decomposition analysis reveals a fairly strong correlation existing between the energy span for the three-component product generation and stabilizing electrostatic interaction within the CuII and X• fragments in CuII-X•.