Laminarin mainly consists of fucoidan, a unique, naturally active sulfate polysaccharide. Laminarin is known for its outstanding multiple bioactives, but its role in lactation remains largely unknown. Therefore, this study aimed to explore the influence of maternal intake of laminarin on lactation and infant health in a porcine model. A total of 20 sows of parity 6.85 ± 0.88 with similar comprehensive scores were randomly allocated to two dietary treatments to receive a basal diet with/without supplementary laminarin. We showed that maternal intake of laminarin improved the antioxidant capacity and intestinal barrier function of the offspring, alleviated the inflammatory response, and facilitated infant growth and health. Mechanistically, maternal consumption of laminarin significantly modified the metabolite profiles of colostrum and milk. We also demonstrated in a vitro study that coniferyl aldehyde, a representative differential milk metabolite, enhanced antioxidant capacity and tight junction protein expression levels in intestinal epithelial cells. In summary, maternal intake of laminarin facilitated offspring health and growth by fortifying milk metabolites.