The role of a service mesh in microservices architecture is to provide a dedicated infrastructure layer that manages service-to-service communication. It handles essential functionalities like load balancing, service discovery, traffic management, and security, without requiring changes to the microservices themselves. This decoupling allows developers to focus on building their applications while the service mesh ensures reliable, secure, and efficient communication between services. By centralizing these management tasks, the service mesh enhances observability and simplifies operations in complex microservices environments.