Venus remains a high-priority target for unraveling the fundamental aspects of climate change and planetary evolution. A robotic lander mission to Venus has the potential of addressing the identified key outstanding scientific goals within the Venus exploration roadmap. Here, we present a new mission concept (‘KYTHERA’) for a long-duration lander system, where we present a new lander design, an entry-descent-landing sequence and corresponding landing site selection and timeline of scientific operations that can support a lander mission of up to 200 Earth days on the Venusian surface. To accommodate the long duration of the mission, the lander was designed with a vacuum-insulated core, cooled and powered by a set of radioisotope-powered Stirling generators. The identified landing site is the Lakshmi Planum region, indicated by a technical and scientific trade off. It was found that a long-duration robotic lander mission to Venus can address most outstanding key science goals outlined in the Venus exploration community. Finally, the results highlight the need for additional studies on the performance and feasibility of instrumentation and materials under Venus’ harsh surface environment.