Despite the existence of internal audit practices, inefficient performance is fast becoming the hallmark of the Nigeria Government Business Enterprises (GBEs). This study therefore examined the effect of internal audit practices on efficient service delivery of GBEs in Ogun State, Nigeria. Anchored on Contingency Theory, the study investigated three dimensions of internal audit: auditor independence, auditor competency, and management support as determinants of cost-efficient service delivery. A survey research design was adopted, targeting a population of 2,235 personnel across fifteen GBEs in Ogun State. Using Yamane's formula, a sample of 340 respondents comprising internal auditors, finance officers, and managers was drawn through simple random sampling, achieving a 96.5% usable response rate. Data were analyzed using Partial Least Squares Structural Equation Modelling (PLS-SEM). Findings revealed that auditor independence (β = 0.298, p < 0.05), auditor competency (β = 0.231, p < 0.05), and management support (β = 0.216, p < 0.05) all exert positive and statistically significant effects on efficient service delivery, with auditor independence emerging as the strongest predictor. The model explained 28.6% of the variance in service delivery efficiency. The study concludes that strengthening internal audit practices through enhanced independence, continuous professional development, and robust management support is critical to improving public service outcomes in Nigerian GBEs.