To identify how variables such as exercise condition, supplementation strategy, participant characteristics and demographics, and practices that control oral microbiota diversity could modify the effect of inorganic nitrate ingestion (as nitrate salt supplements, beetroot juice, and nitrate-rich vegetables) on exercise performance, we conducted a systematic review with meta-analysis. Studies were identified in PubMed, Embase, and Cochrane databases. Eligibility criteria included randomized controlled trials assessing inorganic nitrate on exercise performance in healthy adults. To assess the variation in effect size, we used meta-regression models for continuous variables and subgroup analysis for categorical variables. One hundred and twenty-three studies were included in this meta-analysis totaling 1705 participants. Nitrate was effective for improving exercise performance (Standardized Mean Difference (SMD):0.101; 95% confidence intervals (95%CI):0.051,0.151, P < 0.001, I2 = 0%), although nitrate salts supplementation was not as effective (P = 0.629) as ingestion via beetroot juice (P < 0.001) or a high nitrate diet (P = 0.005). Practices that control oral microbiota diversity influenced the nitrate effect, with practices harmful to oral bacteria decreasing the ergogenic effect of nitrate. Nitrate ingestion was most effective for exercise lasting between 2 and 10min (P < 0.001). An inverse dose-response relationship between the fraction of inspired oxygen and the effect size (coefficient: -0.045;95%CI: -0.085, -0.005, P = 0.028) suggests that nitrate was more effective in increasingly hypoxic conditions. There was a dose-response relation for acute administration (P = 0.049). The most effective acute dose was between 5–14.9mmol provided ≥150min prior to exercise (P < 0.001). An inverse dose-response for protocols ≥ 2days was observed (P = 0.025), with the optimal dose between 5–9.9mmol∙day−1 (P < 0.001). Nitrate, via beetroot juice or a high nitrate diet, improved exercise performance, particular those lasting between 2–10min. Ingestion of 5–14.9mmol⋅day−1 taken at least 150min prior to exercise appears optimal for performance gains, while athletes should be aware that practices which control oral microbiota diversity may decrease the effect of nitrate.