Plastic pyrolysis oil (PPO) is a commercially established product from waste plastic thermal conversion, with global production capacity exceeding 500,000 tonnes annually. However, PPO’s high olefin content (20-60%), oxidative instability (induction period <2 hours), and variable fuel properties limit its direct use as a drop-in fuel. Recent technological advancements in cashew nut shell liquid (CNSL) modification have produced tunable, biobased additives with proven antioxidant, emulsifier, and lubricity-enhancing functions in conventional diesel and biodiesel. This review synthesizes these advancements and demonstrates that CNSL derivatives are directly transferable to PPO upgrading. Evidence from fuel literature confirms that ethoxylated CNSL reduces interfacial tension to ultralow values (10⁻³ mN/m) and stabilizes water-in-fuel emulsions; esterified and natural CNSL extends biodiesel oxidation induction periods by 2 - 5× at 0.1 - 0.5 wt% (Rancimat method); and CNSL - diesel blends (10 - 20%) reduce CO, HC, and smoke emissions while maintaining thermal efficiency comparable to neat diesel. The integration of CNSL with PPO necessitates only formulation optimization, not new chemical discovery. This review critically assesses the established additive technologies, presents transferable performance data, identifies gaps (long-term storage stability, engine durability), and proposes an implementation roadmap. CNSL - PPO blends are a viable low-carbon fuel for stationary engines, industrial burners, and marine applications, as they simultaneously close two waste cycles (plastic waste + cashew shells).