Per- and polyfluoroalkyl substances (PFAS) are a major threat to human health and the environment due to their persistence and harmfulness. One of the most efficient and sustainable approaches for their separation from water is membrane technology. In this study, polyelectrolyte multilayered (PEM) nanofiltration membranes were developed through layer-by-layer assembly of poly(diallyldimethylammonium chloride)/poly(styrenesulfonate) (PDADMAC/PSS) on polyethersulfone (PES) ultrafiltration supports to remove two representative PFAS, perfluorooctanoic acid (PFOA) and perfluorohexanoic acid (PFHxA). The effects of bilayer number and electron beam (EB) surface modification of the PES support were systematically investigated. A membrane coated with two bilayers achieved a PFOA rejection of (90.0 ± 3.6)% with a pure water permeability of (19.6 ± 3.1) L m^-2 h^-1 bar^-1 on unmodified PES, which improved to (94.5 ± 3.2)% and (25 ± 4) L m^-2 h^-1 bar^-1 after EB modification. Increasing the coating to three bilayers further enhanced PFOA rejection to (99 ± 0.4)% with permeability of (16 ± 4.3) L m^-2 h^-1 bar^-1, surpassing the commercial NF270 membrane with (94.6 ± 2.1)% and (15.7 ± 2.5) L m^-2 h^-1 bar^-1). PFHxA rejection was slightly lower due to its smaller molecular size and lower hydrophobicity. The membranes maintained stable rejection across pH values, while salts, particularly MgSO₄ with higher ionic strength, reduced rejection through charge screening and bilayer swelling, which also increased permeability. Overall, PEM membranes, especially those on EB-modified supports, provide a good balance between flux and selectivity and have great potential as scalable, energy-efficient methods of removing PFAS from water.