Liposomes have been reported for combination therapy due to their ability to carry both hydrophilic and lipophilic drugs together. The current investigation aims to develop a novel, eco‐friendly, and sustainable reverse‐phase high‐performance liquid chromatography (RP‐HPLC) method for the simultaneous quantification of capecitabine and celecoxib co‐encapsulated in liposomes. The method reported herein uses a C18 column (4.6 × 250 mm2, 5 μm) and a mobile phase consisting of water, and acetonitrile/methanol in a ratio of 60:40, containing 0.1% formic acid in both the phases. The flow rate is maintained at 1 mL/min, with an injection volume of 10 μL in the gradient mode. Detection is set at λmax = 240 nm for capecitabine and 252 nm for celecoxib. The developed liposomes are mono‐disperse with a surface potential of −6.93 mV. The average size of the liposomes is 142 nm. The percentage entrapment efficiency for capecitabine is 52.39 ± 0.94%, and for celecoxib, it is 77.13 ± 0.74%. The Analytical Greenness Metric of 0.61 and Analytical Eco‐Scale Score of 75 signify the greenness of the developed method. Also, the Red‐Green‐Blue model shows excellent whiteness, with a score of 83.2. Thus, the developed method offers a reliable, accurate, precise, buffer‐free, and environment‐friendly RP‐HPLC approach for the simultaneous analysis of capecitabine and celecoxib co‐encapsulated in liposomes.