The effects of biomaterials on their environment must be carefully modulated in most biomedical applications. Among other approaches, this modulation can be obtained through the modification of the biomaterial surface. This paper proposes a simple and versatile strategy to produce non-leaching antibacterial polylactide (PLA) surfaces without any degradation of the polyester chains. The method is based on a one-pot procedure that provides a "clickable" PLA surface via anionic activation which is then functionalized with an antibacterial quaternized poly(2-(dimethylamino)ethyl methacrylate) (QPDMAEMA) by covalent immobilization on the surface. The anti-adherence and antibiofilm activities of modified PLA surfaces are assessed for different QPDMAEMA molecular weights and different quaternization agents. Antibacterial PLA surfaces are shown to be very active against Gram-negative and Gram-positive strains, with adherence reduction factors superior to 99.999% and a marked reduction in biofilm on the most potent surfaces. In addition to this substantial antibacterial activity, the proposed PLA surfaces are also cytocompatible, as demonstrated through the proliferation of L929 fibroblasts.