This study aimed to investigate the antioxidant potential of bovine casein hydrolysate and a pure peptide screened from it. The casein hydrolysate obtained by pepsin digestion exhibited obvious antioxidant activity in vitro, including potent Fe2+ chelating and 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) cation radical scavenging activities. A novel tetrapeptide, VRYL, was predicted and successfully characterized using in silico techniques and showed excellent ABTS cation radical scavenging ability, with a half maximal inhibitory concentration of 0.36 mg/mL, which is significantly lower than that of the original hydrolysate. Moreover, at the cellular level, VRYL effectively protected against H2O2-induced oxidative stress damage in HepG2 cells and significantly reduced intracellular reactive oxygen species levels. The peptide VRYL not only exhibited excellent antioxidant capacity in vitro but also demonstrated its ability to mitigate oxidative stress damage in a cellular model. This study provides a new theoretical basis for the development of casein hydrolysates and their derived peptides in functional foods.