Background/Objectives: Evidence for herbal ergogenic aids remains uncertain, and ashwagandha trials span heterogeneous performance domains. This review evaluated oral Withania somnifera supplementation on exercise performance and explored participant-, outcome-, formulation-, and supplementation-related moderators. Methods: PubMed, Web of Science, Cochrane Library, Embase, and SPORTDiscus-EBSCO were searched from inception to 1 April 2026. Eligible randomized controlled trials compared oral ashwagandha with placebo or control conditions and reported objective exercise-performance outcomes. Dependent effects were synthesized using restricted-maximum-likelihood three-level random-effects models; 95% prediction intervals, GRADE certainty ratings, subgroup analyses, and dose/duration meta-regressions were reported. Results: Thirteen trials involving 599 participants contributed 79 effect sizes. Samples were mainly young adults or athletes; reported ages included one 18–40-year trial and one late-adolescent athlete cohort aged 17.4 ± 1.7 years. Trial-level sex composition was four male-only, one female-only, three mixed-sex, and five incompletely reported cohorts. Ashwagandha improved overall exercise performance on average (Hedges’ g = 0.47, 95% CI [0.25, 0.69], p < 0.001; I² = 60%; 95% prediction interval [−0.40, 1.33]), but the prediction interval crossed zero. Exercise type was the clearest moderator (P_between = 0.006): evidence was most consistent for aerobic endurance (g = 0.54, 95% CI [0.22, 0.85], p = 0.002), whereas strength effects were positive but uncertain and power or muscular endurance evidence remained sparse. Dose analyses were hypothesis-generating; 500–600 mg/day was the most evidence-supported extract-dose range. Conclusions: Oral ashwagandha may improve selected exercise-performance outcomes, particularly aerobic endurance, but benefits are not uniform across contexts. Future trials should be preregistered, adequately powered, double-blind, formulation-standardized, sex-stratified, and include rigorous blinding checks, mechanistic endpoints, adverse-event monitoring, and sport-specific performance tests.