A Power BI consultant plays a crucial role in data governance by ensuring that data within the Power BI environment is secure, accurate, and compliant with regulatory standards. They help implement role-based access controls, ensuring that sensitive data is only accessible to authorized users. Consultants also assist in setting up data lineage and auditing features to track data usage and modifications. By establishing best practices for data management, consultants ensure that businesses maintain data integrity, reduce risks associated with data breaches, and comply with industry regulations.