Interferon regulatory factors (IRF) are transcription factors that are crucial in various physiological processes, including cell growth, viral infection, and tumor suppression. Among these, IRF1 is activated by interferon-alpha/beta (IFN-α/β) and interferon-gamma (IFN-γ), and it regulates antiviral gene ex- pression via its DNA-binding domain (DBD). In this study, we identified the IRF1 gene in the seven- band grouper, Hyporthodus septemfasciatus, Hse_IRF1, analyzed its expression level across different tissues, and assessed its antiviral activity. The results showed that the open reading frame of the HHse_IRF1 cDNA was 906 bp long and encoded 301 amino acids. The Hse_IRF1 protein possesses a DNA-binding domain typical of the IRF family, containing six conserved tryptophan residues. Previous studies demonstrates that IRF1 lacking the DBD exhibits weakened intrinsic antiviral activity. Therefore, in this study, we designated the IRF1 variant without the DBD as Hse_dIRF1. In vivo experiments revealed that under normal physiological conditions, Hse_IRF1 transcription was highest in the spleen. Moreover, in fish infected with Nervous Necrosis Virus (NNV), IRF1 expression sig- nificantly increased in the spleen from days 2 to 4 post-infection. Furthermore, in SSN-1 cells, Hse_IRF1 expression reduced viral RNA2 replication by approximately 4.64-fold, while the expressing Hse_dIRF1 resulted in only 2.00-fold decrease compared to the control group. These findings suggest that Hse_IRF1 may play an antiviral role in NNV infection, with the DBD of IRF1 contributing to this process. However, further studies are needed to elucidate its association with other immune-re- lated genes involved in the innate immune response of sevenband grouper.