Here we report the use of a tetrabutylammonium decatungstate (TBADT)/thiol photocatalytic system for selective addition of acetone and other simple ketone, nitrile, and chlorocarbon functionalities to terminal olefins. This system avoids the use of energetic reagents such as peroxides and proceeds under mild conditions using Earth-abundant element catalysts, providing a sustainable approach to C–C bond formation using activated olefins. Initial exploration reveals that hydroalkylation of unactivated olefins is also possible, though in lower efficiency, and preliminary mechanistic experiments are consistent with a radical mechanism.