<p><i>Palmaria palmata</i> is a highly nutritious seaweed and a prime candidate for developing sustainable aquaculture of human foodstuff in the North Atlantic, but it faces challenges due to high prices and quality inconsistencies. The present study evaluated the use of hydrogen peroxide (H₂O₂) treatment to consistently enhance the antioxidant capacity of this species. Medium-term (3–7 days), moderate (0.1-1 mM) treatment led to increased phenolic content and antioxidant activity, up to 2.2- and 5.4-fold baseline values, respectively. Proteomics analyses were performed to compare in vitro results to abundances of specific proteins. Increases in antioxidant power were tied to a decrease in growth-related proteins; but were not positively correlated to any specific protein group. These results suggest a medium-term, phenolic-driven response. Additional benefits of H₂O₂ treatment, including its potential for biofouling mitigation, may make this approach highly valuable for improving the quality and consistency of <i>P. palmata</i> and enhancing its valorisation as a functional food and commercial viability.</p>