Aqueous seaweed extracts are a biological product which have beneficial effects on plant growth as well as improving their resistance to several biotic and abiotic stresses. This work aimed to evaluate the effect of aqueous extracts of three seaweeds Fucus spiralis, Cystoseira ericoides (Phaeophyceae) and Ulva lactuca (Chlorophyceae) harvested from Atlantic coast of Rabat region in Morocco, on lead (Pb) tolerance and accumulation in tomato (Solanum lycopersicum) plants. Aqueous extracts were obtained by the combination of 2 extraction processes, ultrasonication and heating. The brown seaweeds F. spiralis and C. ericoides extracts had good antioxidant activity in the DPPH assay. The growth and physiological parameters were compared between Solanum lycopersicum seedlings grown in hydroponic conditions at 0 and 100 μmol Pb with or without 4% seaweed extract. The F. spiralis and C. ericoides extracts significantly increased the aboveground parts and roots biomass compared to control plants treated with Pb alone. In Pb stress conditions, these seaweed extracts enhanced the plant’s tolerance with a reduction of anthocyanin and proline content. F. spiralis extract treatment led to a significant Pb accumulation in aboveground parts of the plant. The effect of U. lactuca extract on tomato plants biomass, anthocyanin and proline was not significant. The study demonstrated that the aqueous extracts of F. spiralis and C. ericoides improved the plant response to heavy metals stress, highlighting the potential use of these seaweeds in phytoremediation processes.