This paper describes the development and validation of a simple reverse phase ultra performance liquid chromatography (RP-UPLC) method for the quantitative determination of 2-(4',4'-Dibromomethylphenyl)benzonitrile impurity content at low level in Irbesartan drug substance. Separation was achieved with 100mm x 2.1mm, 1.7μm particle size, ODS column. The mobile was a gradient prepared by simple phosphoric acid buffer, and Acetonitirle at a flow rate of 0.1 mL min-1, UV detection was performed at 205nm. The method was validated to confirm selectivity, precision, linearity and accuracy parameters as per ICH guideline. Because of its speed and accuracy the detection limit and quantification limit are found to be 0.41 μg ml-1 and 1.46 μg ml-1 respectively. Repeatability is good, with a relative standard deviation of 2.1% to 3.2%. The drug substance was subjected to stability studies as well as stress condition of hydrolysis, oxidation, photolytic, thermal and humidity degradation using optimized method condition to enhance low level of detection within the minimum acquisition time indicating the accuracy of the optimized RP-UPLC method. This simple, efficient methodology can be used for quality control bulk manufacturing as well as routine analysis.