There is evidence to suggest that increasing the level of saturation (that is, the number of sp3-hybridized carbon atoms) of small molecules can increase their likelihood of success in the drug discovery pipeline1. Owing to their favourable physical properties, alkylamines have become ubiquitous among pharmaceutical agents, small-molecule biological probes and pre-clinical candidates2. Despite their importance, the synthesis of amines is still dominated by two methods: N-alkylation and carbonyl reductive amination3. Therefore, the increasing demand for saturated polar molecules in drug discovery has continued to drive the development of practical catalytic methods for the synthesis of complex alkylamines4-7. In particular, processes that transform accessible feedstocks into sp3-rich architectures provide a strategic advantage in the synthesis of complex alkylamines. Here we report a multicomponent, reductive photocatalytic technology that combines readily available dialkylamines, carbonyls and alkenes to build architecturally complex and functionally diverse tertiary alkylamines in a single step. This olefin-hydroaminoalkylation process involves a visible-light-mediated reduction of in-situ-generated iminium ions to selectively furnish previously inaccessible alkyl-substituted α-amino radicals, which subsequently react with alkenes to form C(sp3)-C(sp3) bonds. The operationally straightforward reaction exhibits broad functional-group tolerance, facilitates the synthesis of drug-like amines that are not readily accessible by other methods and is amenable to late-stage functionalization applications, making it of interest in areas such as pharmaceutical and agrochemical research.