Anti-biofouling poly(N-vinyl pyrrolidone) (PVP) coatings with tailored crosslinking degrees were synthesized and grafted onto planar and microporous substrates via a one-step vapor-based approach. N-Vinyl pyrrolidone was copolymerized with ethylene glycol diacrylate at different ratios in the vapor phase, resulting in conformal PVP coatings with a wide spectrum of crosslinking degrees. The synthesized coatings were immobilized onto substrates either through covalent bonding with pretreated surfaces, or by first generating a highly crosslinked polymer prime layer on untreated surfaces, followed by in situ grafting from the reactive sites of the prime coating. The surface hydrophilicity of the resultant coatings along with their protein and bacteria repellency increased monotonically with the decrease of the crosslinking degree. Coatings on planar surfaces with the lowest crosslinking degree showed a water contact angle of 33 ± 1°, comparable to the reported PVP-grafted surfaces, while coatings on microporous membranes exhibited "superwettability" with water contact angles close to 0°. The least crosslinked coatings also adsorbed 92% less bovine serum albumin compared to the control, and readily prevented the attachment of Escherichia coli cells. The grafted coatings are robust against continuous washing and ultrasonication. We expect this vapor-based grafting technique to provide a practical means for imparting surface hydrophilicity and anti-biofouling properties to substrates regardless of their surface chemistry or geometry.