In the current study, white-leg shrimp (Litopenaeus vannamei) were fed on diets containing varying doses of Withania somnifera aqueous extract (WSAE) at a rate of 0 (control), 0.5, 1.0, and 2.0 g/kg feed for 56 days. After the feeding trial, shrimps in all groups were challenged with the exposure to Vibrio harveyi for ten days during which animals' mortality was observed. It is noted that the dietary WSAE linearly and quadratically stimulated shrimp's growth indices particularly at the treatment of 2.0 g/kg feed. Compared to the control group, the WSAE-fed L. vannamei had significantly higher villi length, villi width, and absorption area particularly in the treatment of 2.0 g/kg feed. Furthermore, L. vannamei fed on WSAE-enriched diets consumed more feed and exhibited higher total proteolytic activity, lipase, and α-amylase activities as compared with the control group. The dietary WSAE at escalating levels linearly and quadratically enhanced the antioxidant activity (serum superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), total antioxidant capacity, and reduced glutathione) and the immune response (total hemocyte counts, total protein, lysozyme, and phagocytic activity). Similarly, the mRNA expression levels of cMn-SOD, CAT, and GPx genes were linearly and quadratically upregulated in the hepatopancreas of L. vannamei fed on WSAE-enriched diets (especially in the 2.0 g/kg feed treatment), while their lowest levels were significantly observed in the control group. On the other hand, malondialdehyde levels were significantly decreased in WSAE-supplemented shrimp groups, and its highest levels were observed in animals fed on the control diet. After the bacterial exposure, the survival rates of L. vannamei fed on 1.0 and 2.0 g WSAE/kg feed (61.3% and 66.7%, respectively) were higher than those in the control animals. Taken together, the results obtained herein indicate that inclusion of WSAE in diets of L. vannamei effectively enhanced the growth, antioxidant biomarkers, immune response, and resistance to the V. harveyi infection, particularly at the treatment of 2.0 g/kg feed.