3D printing is seen as a game-changing manufacturing process in many domains, including general medicine and dentistry, but the integration of more complex functions into 3D-printed materials remains lacking. Here, it is expanded on the repertoire of 3D-printable materials to include antimicrobial polymer resins, which are essential for development of medical devices due to the high incidence of biomaterial-associated infections. Monomers containing antimicrobial, positively charged quaternary ammonium groups with an appended alkyl chain are either directly copolymerized with conventional diurethanedimethacrylate/glycerol dimethacrylate (UDMA/GDMA) resin components by photocuring or prepolymerized as a linear chain for incorporation into a semi-interpenetrating polymer network by light-induced polymerization. For both strategies, dental 3D-printed objects fabricated by a stereolithography process kill bacteria on contact when positively charged quaternary ammonium groups are incorporated into the photocurable UDMA/GDMA resins. Leaching of quaternary ammonium monomers copolymerized with UDMA/GDMA resins is limited and without biological consequences within 4–6 d, while biological consequences could be confined to 1 d when prepolymerized quaternary ammonium group containing chains are incorporated in a semi-interpenetrating polymer network. Routine clinical handling and mechanical properties of the pristine polymer matrix are maintained upon incorporation of quaternary ammonium groups, qualifying the antimicrobially functionalized, 3D-printable composite resins for clinical use.