ABSTRACT Remaining Useful Life (RUL) is the length of time a component or system will operate before it requires repair or replacement. Although significant efforts have been made to estimate RUL accurately, controlling RUL remains challenging. This study introduces a state‐space model‐based approach for designing RUL controllers of controlled systems in degradation. It explores the relationship between a system's operational dynamics and its ongoing aging process, particularly the degradation rate experienced by a component during a given operational condition. In this approach, the RUL control problem is formulated as the problem of controlling a polytopic uncertain system. Therefore, robust design methods are proposed for both state observation and control to manage the degradation trajectory, ensuring an acceptable level of deterioration within a desired average lifetime. To illustrate its applicability, the proposed approach is implemented in a variable‐speed wind turbine, with a flexible shaft subject to torsional effects. The results highlight the benefits of using RUL control to enhance the durability of controlled systems while maintaining production performance and demonstrate the effectiveness of such an approach for managing the system's end‐of‐life.