This study examined the ability of the green microalgaeChlorella vulgaristo remove arsenic from aqueous solutions. A series of studies was conducted to determine the optimal conditions for biological arsenic elimination, including biomass amount, incubation time, initial arsenic level, and pH values. At 76 min, pH 6, 50 mgL−1metal concentration, and 1 gL−1bio-adsorbent dosage, the maximum removal of arsenic from an aqueous solution was 93%. The uptake of As (III) ions byC. vulgarisreached an equilibrium at 76 min of bio-adsorption. The maximum adsorptive rate of arsenic (III) byC. vulgariswas 55 mg/gm. The Langmuir, Freundlich, and Dubinin–Radushkevich equations were used to fit the experimental data. The best theoretical isotherm of Langmuir, Freundlich, or/and Dubinin–Radushkevich for arsenic bio-adsorption byChlorella vulgariswas determined. To choose the best theoretical isotherm, the coefficient of correlation was used. The data on absorption appeared to be linearly consistent with the Langmuir (qmax= 45 mgg−1; R2= 0.9894), Freundlich (kf= 1.44; R2= 0.7227), and Dubinin–Radushkevich (qD–R= 8.7 mg/g; R2= 0.951) isotherms. The Langmuir and Dubinin–Radushkevich isotherms were both good two-parameter isotherms. In general, Langmuir was demonstrated to be the most accurate model for As (III) bio-adsorption on the bio-adsorbent. Maximum bio-adsorption values and a good correlation coefficient were observed for the first-order kinetic model, indicating that it was the best fitting model and significant in describing the arsenic (III) adsorption process. SEM micrographs of treated and untreated algal cells revealed that ions adsorbed on the algal cell’s surface. A Fourier-transform infrared spectrophotometer (FTIR) was used to analyze the functional groups in algal cells, such as the carboxyl group, hydroxyl, amines, and amides, which aided in the bio-adsorption process. Thus,C. vulgarishas great potential and can be found in eco-friendly biomaterials capable of adsorbing arsenic contaminants from water sources.