ESG assurance is rising globally and is expected to become mandatory as regulatory frameworks evolve. ESG reporting is the disclosure of company information regarding its environmental, social, and governance (ESG) performance, and it is aimed at increasing transparency and accountability to stakeholders. ESG assurance is a specialized service provided by qualified and independent professionals to assess the quality of ESG reporting by companies. ESG assurance comes at a cost that affects the financial performance of companies. This study aims to investigate and identify the impact of ESG assurance on financial performance through the systemic review of literature and the review of annual financial statements of the top 10 Johannesburg Stock Exchange (JSE)-listed companies in the years 2022 and 2023. A quantitative analysis of the impact of ESG assurance on financial performance will be assessed. The study revealed that ESG assurance is an integral part of the combined assurance model, and there are concerns regarding the assurance processes, costs, and the lack of control over the reliability of the ESG disclosures. This research provides evidence of the complex relationship between ESG assurance and financial performance. The study concluded that ESG reports are relevant for investors and other stakeholders if the information is reliable. Although ESG reporting comes at a cost, companies purchase ESG assurance to indicate the quality of ESG reporting and demonstrate their commitment to managing ESG issues. However, it negatively impacts a company’s financial performance in the short term. This article contributes to ESG literature by empirically examining the underexplored relationship between ESG assurance and firm performance in small South African firms.