Solid-state fermentation represents a sustainable approach for the conversion of agro-industrial wastes into high-added-value feed ingredients. The present study aimed to evaluate the effects of the dietary addition of a solid-state-fermented mixture of olive mill stone waste (OMSW) and Lathyrus clymenum husks (LP) on the antioxidant blood parameters of weaned piglets. Two hundred 35-day-old weaned piglets were allotted into two groups and fed either a control (C) diet or a diet containing 50 g of OMSW-LP per kg (OMSW-LP) for 40 days. Blood samples were collected at 35 and 75 days of age to assess the free radical scavenging activity (FRSA), reduced glutathione (GSH) levels, catalase activity (CAT), protein carbonyls (CARBs), and thiobarbituric acid reactive species (TBARS). The OMSW-LP diet reduced the TBARS (p = 0.049) and CARB contents (p = 0.012) and increased the levels of FRSA (p = 0.005), GSH (p = 0.040), and CAT activity (p = 0.012) in the piglets' blood, likely due to the synergistic action of the antioxidants and bioactive compounds present in the OMSW-LP mixture. Overall, the dietary inclusion of solid-state-fermented OMSW-LP at 50 g/kg could potentially serve a bio-functional purpose since it enhanced the antioxidant blood parameters in this study, a crucial factor for the health and growth of piglets post-weaning.