The remarkable catalytic potential of enzymes in chemical synthesis, environmental bioremediation and medical therapeutics is limited by their longevity and stability. Immobilization of enzymes on solid supports has been demonstrated to improve the stability of biocatalysts, but often relies on multiple chemical steps for covalent attachment and is limited by the physical properties of the various supports. Here, we describe production of enzyme:hydrogel complexes via engineering of a cationic supercharged phosphotriesterase. These enzyme:hydrogel complexes are remarkably robust with no loss of catalytic activity over 100 days, have high activity, with turnover numbers of up to 105 when used in a flow reactor at catalyst loadings as low as 0.0008 mol%, and display exceptional resilience to organic solvents. These enzyme:hydrogel complexes are likely to have value in diverse applications such as enantioselective continuous-flow chemistry, detoxification of poisons, and the formation of functionalized biomaterials.