Chimeric antigen receptor (CAR) natural killer (NK) cell immunotherapy offers a promising approach against cancer. However, the molecular mechanisms that regulate CAR-NK cell activity remain unclear. Here we identify the transcription factor cyclic AMP response element modulator (CREM) as a crucial regulator of NK cell function. Transcriptomic analysis revealed a significant induction of CREM in CAR-NK cells during the peak of effector function after adoptive transfer in a tumour mouse model, and this peak coincided with signatures of both activation and dysfunction. We demonstrate that both CAR activation and interleukin-15 signalling rapidly induce CREM upregulation in NK cells. Functionally, CREM deletion enhances CAR-NK cell effector function both in vitro and in vivo and increases resistance to tumour-induced immunosuppression after rechallenge. Mechanistically, we establish that induction of CREM is mediated by the PKA-CREB signalling pathway, which can be activated by immunoreceptor tyrosine-based activation motif signalling downstream of CAR activation or by interleukin-15. Finally, our findings reveal that CREM exerts its regulatory functions through epigenetic reprogramming of CAR-NK cells. Our results provide support for CREM as a therapeutic target to enhance the antitumour efficacy of CAR-NK cells.