Research interest in thriving at work has burgeoned over the past decades, but we still know little about how HR practices affect employees’ thriving. Drawing on self-determination theory and P-O fit theory, we developed and tested a moderated mediation model to explain how fun HR practices enhance employee thriving at work. Data collected from two studies, a scenario experiment (N = 164) and a time-lagged survey (N = 253), provided support for our hypotheses. Specifically, our results revealed that fun HR practices positively predict employee thriving at work and this relationship is mediated by autonomous motivation. Further, fun HR practices translate into higher autonomous motivation and subsequent thriving when employees have higher preference for workplace fun. This research contributes by providing a more nuanced understanding of the psychological process through which HR practices affect employee outcomes, and how HR practices benefit employees contingent upon individual characteristics. Implications for practice, limitations and future research directions are then discussed.