A user terminal for controlling a display device and a control method thereof are provided. The user terminal includes a communicator configured to communicate with the display device, a main controller configured to control the user terminal, and a sub-controller configured to control the user terminal while the user terminal is in a sleep mode, wherein the sub-controller is configured to change a mode of the user terminal from the sleep mode to a standby mode in response to the communicator receiving environmental change detection information or user detection information from the display device while the user terminal is in the sleep mode.