The Thermal Management Integrated System (TheMIS) is a key element of the payload of the Australia-Italy Space Industry Responsive Intelligent Thermal (SpIRIT) mission. SpIRIT is a collaborative effort led by the University of Melbourne between the Australian space industry, academia and the Italian Space Agency to promote cooperation in space exploration and further the maturity of the Australian space sector. Part of a broader University of Melbourne R&D focus on advanced remote sensing from nanosatellites, TheMIS has the ability to both actively cool and control the temperature of sensitive instruments, opening up the potential for more capable payloads on small spacecraft systems. This capability is achieved using a Commercial off-the-shelf (COTS) Stirling Cycle Cryocooler, in-house developed control electronics, pyrolytic graphite sheet thermal straps and deployable radiators, including a hold down and release mechanism. To date, this degree of thermal control has not been used on small spacecraft systems, however, with advances in cooling technology and spacecraft components, the ability to increase the performance of sensors through active cooling is opening up. To give the system a development focus and demonstrate its capability in a real‐world example, TheMIS will manage the thermal environment of SpIRIT’s HERMES payload, an X-ray instrument that will be provided by the Italian Space Agency. However, beyond this mission, TheMIS has the potential to support multiple other applications such as low-noise infrared imaging and increased resilience of electronics to space weather. TheMIS aims to provide the space industry with a technology that is seen as a key product to improve sensor performance in a range of different areas. The SpIRIT project has designed and developed a 6U CubeSat mission that will provide the opportunity for TheMIS to gain flight heritage. This paper discusses the TheMIS design and implementation, and summarizes the outcomes of subsystem thermal testing, leading to the integration in the payload suite and the spacecraft as a whole.