The primary function of a microcontroller is to act as a compact integrated circuit designed to govern a specific operation in embedded systems. Microcontrollers combine a processor, memory, and input/output peripherals on a single chip, allowing them to control various devices and processes. They are commonly used in applications such as automotive systems, home appliances, and industrial machines. The ability to perform dedicated tasks efficiently makes microcontrollers crucial for automating and enhancing functionality in numerous devices.