Research indicates that university instructors struggle with compromised subjective well-being (SWB) and have faced further challenges due to the COVID-19 pandemic. Although studies have found instructors' achievement goals to be important motivational factors linked to their well-being, longitudinal research is needed to clarify the directionality of these relations over time to advance theory, research, and practice. In the present study, we aimed to contribute to this line of research by investigating bidirectional relations between achievement goals and multifaceted SWB (positive affect, negative affect, job satisfaction, life satisfaction) in 489 German university instructors across a semester (3 months) during the COVID-19 pandemic. Latent cross-lagged panel analysis revealed that instructors' positive affect and job satisfaction at the semester start positively predicted changes in their mastery approach goals and performance approach goals, and negatively predicted changes in their work avoidance goals. Moreover, a positive reciprocal loop was observed between job satisfaction and performance approach goals. Our findings emphasize the necessity of considering instructors' achievement goals not only as causes but also as consequences of their well-being when designing future studies and support measures.Educational Impact and Implications StatementUniversity instructors play an important role in higher education institutions through their teaching; however, they have been found to struggle with issues such as stress and burnout. To better understand how to support instructors, the present study examined how their individual motivations (in the form of their achievement goals) were related to their well-being over time. The results showed that instructors who experienced greater happiness and satisfaction in their teaching role at the semester start placed a stronger focus on performing their teaching tasks well, improving and expanding their professional competencies and knowledge, and appearing competent in their teaching. Additionally, those focused on appearing competent also experienced greater job satisfaction, creating a positive feedback loop. Consequently, initiatives aimed at supporting university instructors should prioritize their well-being as a means of promoting healthy goal pursuit.