Aim: Bosutinib (BST) is an anti-cancer medicine that is used to treat a variety of different types of cancer. Using the HPLC method of analysis and the Quality by Design (QbD) strategy, the study aimed to precisely quantify the drug in tablet form and in rat plasma. Methodology: For the developed method’s validation, the chromatographic settings were fine-tuned by making use of the Box–Behnken Design (BBD). In the BBD, two dependent variables and three independent variables were selected. Isocratically, samples were eluted, having eluent phase composition of ammonium acetate (CH3COONH4) buffer pH 3.0 and acetonitrile (CH3CN) (60:40% v/v), in Raptor C-18 column at temperature 25 ∘C with a flow rate of 1 mL/min for 5 min. The wavelength of detection was set at 260 nm. In this study, encorafenib (ENC) was employed as an internal standard. Result: A sharp and resolved peak of BST and ENC at a retention time of 1.92 min and 4.01 min, respectively, was observed by the developed method. The limits of quantification and detection of the newly established method were found to be 1.503 μg/mL−1 and 0.496 μg/mL−1. The calibration curve’s observed linearity range was between 2 and 20 μg/mL−1, with an r2 of 0.999. The developed and optimized method was verified in compliance with the ICH guidelines. The results of all validation parameters were within the acceptable range, for example, % RSD of system suitability (0.63–4.46), % RSD of linear regression (1.659), interday and intraday precision % RSD value (1.723–1.892), and (1.762–1.923), respectively, and accuracy (1.476–1.982). Conclusion: The quantity of BST in tablet dosage form and in rat plasma samples was determined using a simple, quick, and robust method that was devised and validated.