Poly (vinylidene fluoride) (PVDF) based membranes are inert and hydrophobic, which makes them susceptible to biofouling. Blending it with a biopolymer like Poly (butylene succinate-co-adipate) (PBSA) can offer functional sites to tether anti-microbial and anti-fouling agents to improvise the anti-bacterial and anti-fouling properties of PVDF. In this study porous PVDF/PBSA membranes were obtained using non-solvent induced phase separation and modified by a unique phosphonium chloride trihexyltetradecylphosphonium chloride by two approaches. In the first approach; phosphonium chloride was immobilized onto the porous membrane while in the second, the membrane was tethered with graphene oxide initially and then immobilized by phosphonium chloride leading to synergistic performance towards excellent antibacterial and antifouling characteristics. The antimicrobial action manifested by the modifications was assessed by standard plate count taking E.coli and S.aureus as model bacterial organisms. To understand the antimicrobial mechanism, outer membrane permeabilization studies with N-Phenyl-1-naphthylamine assay, intracellular leakage of K+ ion and nucleic acids in metabolic pool and intracellular Reactive oxygen species (ROS) generation studies were assessed. The antifouling study was also carried out by using Bovine serum albumin (BSA) as a model biofoulant. This study demonstrated high distilled water flux, excellent fouling resistance, impressive 7-fold reduction of bacteria and stable flux performance. © 2017 Elsevier B.V.