This study combined a multilevel assessment to analyse the effect of Ocean acidification and Marine Heat waves (MHW) on P. oceanica seedlings. The main goal was to explore if OA acclimated seedlings are more resistant to future MHW. Results demonstrated that prolonged OA exposure will enhance the physiological response of P. oceanica seedlings to MHW. Seedlings exposed to long-term OA conditions were able to specifically regulate the antioxidant system and the whole transcriptomic machinery to better counteract thermal stress effects. The benefiacial effect induced by acidification in the coming decades could reverse the negative effects imposed by sea warming, making P. oceanica more resilient against global environmental stressors.