This study investigated the bioactive compounds, antioxidant and antimicrobial properties of three microalgal species: Spirulina platensis, Scenedesmus obliquus, and Chlorella vulgaris, to evaluate their potential as natural bioactive agents. The antioxidant activity was assessed using free radical scavenging (DPPH) and Ferric Reducing Antioxidant Power (FRAP) assays. At the same time, antimicrobial efficacy was tested against various pathogens, including Gram-positive and Gram-negative bacteria and fungi. The three algae were also screened for their phyco-pigment content including chlorophyll, carotenoids, phycocyanin, allophycocyanin, and phycoerythrin. The bioactive composition of the three microalgal species was determined by gas chromatography-mass analysis. The data revealed that Spirulina platensis exhibited the highest DPPH radical scavenging activity (70.35% inhibition at 200mg/ L), linked to its abundant phycocyanin, chlorophyll, and carotenoid content. Scenedesmus obliquus demonstrated the highest ferric reducing power (maximum absorbance 1.1239), likely due to its high concentration of chlorophyll b and fatty acids, which support electron donation and antioxidant activity. The GC-MS analysis identified the key bioactive compounds in each algal species, including polyunsaturated fatty acids, flavonoids, and terpenes, contributing to their antioxidant and antimicrobial effects. Spirulina platensis showed the strongest antimicrobial activity against Bacillus subtilis and Candida albicans, while Scenedesmus obliquus was most effective against Staphylococcus aureus and Escherichia coli. These findings highlight the potential of these microalgae as natural sources of antioxidants and antimicrobials, with promising applications in pharmaceuticals, food preservation, and managing antimicrobial resistance.