<p>The main objective of this study is to investigate the effect of accelerated weathering on the mechanical behaviour, failure modes, and service life of alkali-treated hemp fibre-reinforced composites with interpenetrating polymer networks (IPNs) developed with commercial epoxy and a bio-epoxy obtained from epoxidized waste rice bran oil (ERBO). The bio-resin (<i>B</i>) was blended with commercial epoxy (<i>C</i>) in ratios from 100<i>C</i>:0<i>B</i> to 50<i>C</i>:50<i>B</i> to form IPN matrices, which were characterized through chemical, thermal, and rheological analyses. FTIR and ¹H NMR confirmed successful epoxidation, while the resin exhibited shear-thinning flow behaviour and showed endothermic curing peak at 119&#xa0;°C from DSC. Composites fabricated by hand lay-up were exposed to weathering for 500 and 1008&#xa0;h at 60&#xa0;°C, 0.7 W/m² UV intensity, and 100% relative humidity, followed by mechanical evaluation. The 90<i>C</i>:10<i>B</i> system showed the highest initial tensile, flexural, and interlaminar shear strengths (ILSS), which decreased 13.69%, 23.12%, and 9.79% after weathering, accompanied by a shift towards more elastic failure. Fractography revealed lower void content and reduced moisture uptake-about 3 wt.% less than the 100<i>C</i>:0<i>B</i> system. Service-life estimates based on 50% strength retention suggested useful durations of 3.73, 2.80, and 5.25&#xa0;years for tensile, flexural, and ILSS performance.</p> Graphical Abstract <p></p>