Trans-resveratrol’s (trans-RES) therapeutic potential is limited by poor bioavailability and photolability. We developed and validated a robust RP-HPLC method, in accordance with the ICH M10 guideline, for the quantification of trans-RES in plasma. Excellent chromatographic separation of the trans- and cis-isomers was achieved using a liquid–liquid extraction procedure, followed by isocratic elution with a mobile phase consisting of 0.05% formic acid in water–acetonitrile (40:60, v/v). The method demonstrated high linearity (R2 > 0.999) over the concentration range of 0.025 to 50 μg/mL. The method also demonstrated precision (%CV < 5%), accuracy (93.90–98.19%), and sensitivity (LLOQ 0.025 μg/mL). Stability studies confirmed trans-RES’s susceptibility to ultraviolet (UV)-induced isomerization, necessitating the implementation of photostability controls. The method’s environmental impact was evaluated using the Analytical GREEnness (AGREE) metric, yielding a favorable score of 0.7 that highlights its alignment with green chemistry principles. This fully validated protocol was successfully applied in the first comprehensive pharmacokinetic study comparing five administration routes in rats. Intraperitoneal administration yielded the highest bioavailability (84.92 ± 4.87%), significantly exceeding that of the oral route (4.91 ± 0.22%). Flip-flop kinetics observed for all nonintravenous routes indicated absorption-limited disposition. The validated method thus provides a reliable, sustainable bioanalytical tool, while the pharmacokinetic insights underscore the imperative for strategic formulation development to overcome bioavailability and stability limitations, thereby advancing the translational potential of trans-RES. © 2026 The Authors. Published by American Chemical Society