Ketones are crucial intermediates in synthesis and frequent moieties in many products. The direct regioselective synthesis of ketones from internal alkenes could simplify synthetic routes and solve a long-standing challenge in catalysis. Here we report the laboratory evolution of a cytochrome P450 enzyme for the direct oxidation of internal arylalkenes to ketones with several thousand turnovers. This evolved ketone synthase benefits from 15 crucial mutations, most of them distal to the active site. Computational analysis revealed that all these mutations collaborate to generate and tame a highly reactive carbocation intermediate. This is achieved through a confined, rigid, and geometrically and electrostatically preorganized active site. The engineered enzyme exploits a metal–oxo species for ketone synthesis and enables various challenging alkene functionalization reactions. This includes the catalytic, enantioselective oxidation of internal alkenes to ketones and formal asymmetric hydrofunctionalizations of internal alkenes in combination with other biocatalysts.