The function of a service mesh in microservices architecture is to manage the communication between various microservices. A service mesh provides a dedicated infrastructure layer that facilitates service-to-service interactions, enhancing features like load balancing, service discovery, security, and monitoring. By decoupling these functionalities from the business logic of microservices, a service mesh simplifies the development and deployment process. It enables developers to focus on business functionality while ensuring seamless connections and resilience in communication between services, improving overall reliability and scalability.