Cooperative catalytic systems are making significant advances in modern organic synthesis due to the potential to combine multiple catalytic cycles or enable enzyme-like proximity effects. We report the rational design of a bifunctional helical peptide catalyst that displays an imidazolidinone catalyst in close proximity to a thiourea binding site and enables proximity-enhanced reactivity and selectivity. The helical structure of the peptide and the binding of both reactants are shown to be essential for enhanced reactivity in Diels–Alder and indole alkylation reactions, and up to 28 000 catalyst turnovers are achieved. A variety of Lewis basic functional groups facilitate binding and proximity-enhanced reactivity, and product selectivity is observed that cannot be achieved in the absence of the peptide template.