Extreme careerism has become increasingly prevalent in modern workplaces, posing a challenge to the sustainable development and long-term survival of organizations. Guided by Conservation of Resources (COR) theory, this study investigates how careerism contributes to work alienation and presenteeism. It proposes a moderated mediation model in which work alienation mediates the relationship between careerism and presenteeism. Additionally, it explores how perceived motivational climate—specifically mastery and performance climates—moderates this relationship. The study collected data from 330 employees across public and private sectors in the Seoul metropolitan area, using convenience sampling. Hayes’s PROCESS macro was used to test the proposed model. Results show that work alienation fully mediates the effect of careerism on presenteeism. Notably, mastery climate strengthens the indirect effect of careerism on presenteeism through work alienation—contrary to initial expectations. By identifying key psychological mechanisms that exacerbate presenteeism, this study offers practical recommendations to reduce productivity loss. It also broadens the theoretical understanding of destructive workplace behaviors and contributes to future research on career-driven organizational dynamics.