A mild and direct strategy for the construction of aryl aminooxetanes has been accomplished through the synergistic combination of photoredox and nickel catalysis. This approach represents a rare example of harnessing challenging tertiary radicals in photoredox/nickel cross-coupling. Oxetanes are often employed in medicinal chemistry as carbonyl or gem-dimethyl bioisosteres, but their accessibility is hampered by the lack of practical synthetic methods. The strategy reported here utilizes a readily available oxetanyl amino acid building block in a cross-coupling manifold to rapidly access oxetane scaffolds with broad functional group tolerance. Computational studies reveal that a catalytic cycle beginning with Ni(0)–Ni(II) oxidative addition, rather than radical addition to Ni(0), is operative for reactions with aminooxetanyl radicals. Consequently, for radical-based photoredox/nickel-catalyzed cross-couplings, the preferred mechanistic pathway has a fundamental dependence on the identity of the radical.