Background: Prostate cancer (PCa) risk is understood to be mostly unmodifiable and inherited, but there is evidence that environmental and behavioral factors may also contribute. A recent study of health professional cohorts suggests a healthy lifestyle can mitigate a high inherited risk of lethal PCa. It is unknown how modifiable factors affect PCa risk in more diverse populations. Our objective was to determine the effects of healthy lifestyle and Agent Orange exposure on PCa risk when accounting for race/ethnicity, family history, and genetic risk in a diverse population. Methods: The Million Veteran Program (MVP) is a national, population-based cohort study of United States military veterans conducted 2011-2021 with 590,750 male participants available for analysis. Healthy lifestyle was quantified as: A healthy lifestyle score (range 0-3) was calculated with a point assigned for each of the following at MVP enrollment: not a current smoker, body mass index (BMI) 30 and strenuous activity 2 days per week. Agent Orange exposure was obtained from VA records. Genetic risk was assessed via a polygenic hazard score using genotype data. Results: Healthy lifestyle was independently associated with reduced metastatic PCa (HR 0.82, 95% CI 0.77–0.87, p<0.001) and fatal PCa (HR 0.76, 95% CI 0.68–0.86, p<0.01) when accounting for family history, genetic risk, and race/ethnicity. The benefit of healthy lifestyle was also observed in Black participants on subset analysis. Agent Orange exposure was an independent factor for PCa diagnosis (HR 1.06, 95% CI 1.04-1.09). Conclusions: Adherence to a healthy lifestyle is associated with reduced risk of metastatic or fatal PCa, which offsets inherited risk.