Algae are an important raw material for the bio-based economy due to their unique content of bioactive compounds. Therefore, this study aimed to evaluate simple applicable extraction methods of the brown seaweed Sargassum swarttzii and identify some of its bioactive phytocomponents using a Gas Chromatography-Mass Spectrometry of the most effective extract. Serial concentrations from the three different S. swartzii extracts; autoclaved water extract (SAWE), ethanolic extract (SEE) and cold water extract (SCWE ) were compared for their effect on seed germination of two economic crops in Egypt; fenugreek (Trigonella foenum-graecum L.) and barley (Hordeum vulgare L.). The total carbohydrates, protein and lipid contents were estimated for the algal biomass; in addition, the total phenolics, total flavonoids and total antioxidant activity were evaluated. The results proved that the SCWE enhanced seed germination of both plants by 5.9% in fenugreek and barely, respectively. The SCWE improved the seedling length by 59.3% at 20% SCWE and 41.6% at the concentration of 40% SCWE in fenugreek and barely, respectively. Moreover, the bioactive compounds and the total antioxidant activity increased significantly in the SCWE over the SAWE and SEE. On top of the 32 bioactive phytocomponents detected by the GC-MS of SCWE were palmitic acid, alpha-ionone, oleic acid, triacetin and lucenin-2. Thus, SCWE could be a promising alternative to harmful synthetic antioxidants and biofertilizers.