Display omitted •PAN membranes were formed using co and post hydrolysis to host PA layer.•Co-hydrolysis resulted in fine microvoidal morphology of PAN support.•Co-hydrolysis of PAN resulted in formation of ideal polyamide layer (O/N ∼ 1).•PA-HPAN-Co exhibited improved pervaporation flux for simulated brine. A novel method of co-hydrolysis of polyacrylonitrile (PAN) support to host polyamide (PA) formation using coactive delayed phase inversion is presented to synthesize high-performance pervaporation membranes. Pure water in the coagulation bath was replaced with a 1.0 M sodium hydroxide solution maintained at 50 °C, allowing concurrent hydrolysis and delayed phase inversion. The characterization results revealed a smoother surface morphology, a higher carboxylic group content, improved hydrophilicity, and an ideal O/N ratio (∼1) of the PA layer on the co-hydrolyzed PAN (HPAN-Co) support compared with the PA layer on the post-hydrolyzed PAN (HPAN-Post) support. Furthermore, the typical pattern observed in PA-HPAN-Post, with a plethora of finger-like pores followed by macrovoids, completely disappeared and was replaced by a uniform and fine microvoid structure in PA-HPAN-Co, with an approximately 50 % reduction in membrane thickness. This led to a reduction in membrane swelling and salt transport without compromising the permeation flux. The pervaporation tests with a 10 wt% NaCl feed at 70 °C using PA-HPAN-Co showed a 99.97 % salt rejection ability and a 74.2 kg m−2h−1 flux, which is 33 % higher than the permeate flux of PA-HPAN-Post. Thus, the PA-HPAN-Co membrane is highly recommended for pervaporative desalination, considering the enhanced performance and scalability of the synthesis technique.