A stability‑indicating reverse phase high performance liquid chromatography method was developed and validated for Levothyroxine and Liothyronine. The wavelength selected for quantitation was 285 nm. The method has been validated for linearity, accuracy, precision, robustness, limit of detection and limit of quantitation. Linearity was observed in the concentration range of 10-100 µg/ml for both drugs. For RP‑HPLC, the separation was achieved by C-18 column (Phenomenax, 250 x 4.6 mm i.d.) coupled using in mobile phase Acetonitrile: Water (25:75) as mobile phase with flow rate 1 ml/min. The retention time of Levothyroxine and Liothyronine were found to be 2.08 min and 5.02 min, respectively. During force degradation, drug product was exposed to hydrolysis (acid and base hydrolysis), H2O2, thermal degradation and photo degradation. The percent degradation was found to be 10 to 20% for both Levothyroxine and Liothyronine in the given condition. The method specifically estimates both the drugs in presence of all the degradants generated during forced degradation study. The developed methods were simple, specific and economic, which can be used for simultaneous estimation of both drugs in any combination of dosage forms.