Bacterial biofilms are often difficult to treat and represent the main cause of chronic and recurrent infections. In this study, we report the synthesis of a novel antimicrobial/antibiofilm polymer that consists of biocompatible oligoethylene glycol, hydrophobic ethylhexyl, cationic primary amine, and nitric oxide (NO)-releasing functional groups. The NO-loaded polymer has dual-action capability as it can release NO which triggers the dispersion of biofilm, whereas the polymer can induce bacteria cell death via membrane wall disruption. By functionalizing the polymers with NO, we observed a synergistic effect in biofilm dispersal, planktonic and biofilm killing activities against Pseudomonas aeruginosa. The NO-loaded polymer results in 80% reduction in biofilm biomass and kills >99.999% of planktonic and biofilm P. aeruginosa cells within 1 h of treatment at a polymer concentration of 64 μg mL-1. To achieve this synergistic effect, it is imperative that the NO donors and antimicrobial polymer exist as a single chemical entity, instead of a cocktail physical mixture of two individual components. The excellent antimicrobial/antibiofilm activity of this dual-action polymer suggests the advantages of combination therapy in combating bacterial biofilms.