Platelets have a limited shelf life, due to the risk of bacterial contamination and platelet quality loss. Most platelet storage bags are made of a mixture of polyvinyl chloride with a plasticizer, denoted as pPVC. To improve biocompatibility of pPVC with platelets and to inhibit bacterial biofilm formation, an antifouling polymer coating is developed using mussel‐inspired chemistry. A copolymer of N,N‐dimethylacrylamide and N‐(3‐aminopropyl)methacrylamide hydrochloride is synthesized and coupled with catechol groups, named DA51‐cat. Under mild aqueous conditions, pPVC is first equilibrated with an anchoring polydopamine layer, followed by a DA51‐cat layer. Measurements show this coating decreases fibrinogen adsorption to 5% of the control surfaces. One‐step coating with DA51‐cat does not coat pPVC efficiently although it is sufficient for coating silicon wafers and gold substrates. The dual layer coating on platelet bags resists bacterial biofilm formation and considerably decreases platelet adhesion. A cationic antimicrobial peptide, E6, is conjugated to DA51‐cat then coated on silicon wafers and introduces bactericidal activity to these surfaces. Time‐of‐flight second ion‐mass spectroscopy is successfully applied to characterize these surfaces. pPVC is widely used in medical devices; this method provides an approach to controlling biofouling and bacterial growth on it without elaborate surface modification procedures.