Glycine max (L.) Merrill (soybean) is a major leguminous crop, cultivated globally as well as in Iran. This study examines the chemical composition of soybean essential oil, and evaluates the antioxidant and antimicrobial activities of seeds on various plant pathogens that commonly cause irreparable damages to agricultural crops. The essential oil of soybean seeds was analyzed by gas chromatography coupled to mass spectrometry. Antimicrobial activity was tested against 14 microorganisms, including three gram-positive, five gram-negative bacteria, and six fungi, using disk diffusion method and the Minimum Inhibitory Concentration technique. The soybean seeds were also subjected to screening for possible antioxidant activity by using catalase, peroxidase, superoxide dismutase, and 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay. Forty components were identified, representing 96.68% of the total oil. The major constituents of the oil were carvacrol (13.44%), (E,E)-2,4-decadienal (9.15%), p-allylanisole (5.65%), p-cymene (4.87%), and limonene (4.75%). The oil showed significant activity against Pseudomonas syringae subsp. syringae, Rathayibacter toxicus with MIC = 25 µg/mL, and Pyricularia oryzae with MIC = 12.5 µg/mL. In addition, the free radical scavenging capacity of the essential oil was determined with an IC50 value of 162.35 µg/mL. Our results suggest that this plant may be a potential source of biocide, for economical and environmentally friendly disease control strategies. It may also be a good candidate for further biological and pharmacological investigations.