Spring viraemia of carp virus (SVCV) is a major threat to the aquaculture industry, causing severe economic losses and significantly impacting fish health. Despite this, no approved antiviral treatments are currently available for use in aquaculture, underscoring the urgent need for effective interventions. This study evaluated the antiviral and immunomodulatory potential of Schisandrin A (SA), a bioactive compound derived from the traditional Chinese medicinal herb Schisandra chinensis, against SVCV. Through a combination of in vitro and in vivo experiments, SA was found to significantly inhibit SVCV replication, lower the viral titer, and improve survival rates in infected juvenile carp. Mechanistically, SA enhanced the host’s innate immune response, as demonstrated by the upregulation of key antiviral genes including interferon-alpha1 (ifna1), interferon-gamma (ifnγ), interferon-stimulated gene 15 (isg15), and myxovirus resistance 1 (mx1). Additionally, SA exhibited potent antioxidative properties, preserving mitochondrial integrity and reducing oxidative stress in SVCV-infected cells. These findings showed the dual role of SA in both directly suppressing viral replication and modulating the immune response, offering a multifaceted approach to managing SVCV infection. Given its low toxicity and biodegradability, SA emerges as a promising, sustainable antiviral agent for aquaculture. This study highlights the potential of SA to enhance biosecurity and promote sustainability in the industry, paving the way for the development of eco-friendly antivirals that could improve the management of viral diseases, ensuring healthier fish populations and greater economic stability.