Example approaches for customization of thermal and power policies in computers, are described. In an example, a microcontroller of a computing system, also referred to as system, validates thermal policy custom data stored in a firmware storage medium of the system, in response to a supply of power to the system. On a successful validation of the thermal policy custom data, thermal control settings is updated with a customized thermal policy included in the thermal policy custom data. In response to initiation of a boot operation of the system, a processor of the system validates power policy custom data stored in the firmware storage medium. In response to a successful validation of the power policy custom data during the boot operation, the processor updates power control settings of the system with a customized power policy included in the power policy custom data.