The green synthesis of silver nanoparticles using Cyamopsis tetragonoloba plant extract and their photocatalytic and antibacterial properties is reported. Three precursor concentrations of 1 mM, 2 mM and 5 mM were used, and at two different ratios of 1:5 and 1:10 plant extract to the precursor. The formation of the nanoparticles was followed by the periodic study of surface plasmon resonance using the UV-visible spectroscopy, which revealed the formation of nanoparticles with regular bands after 45 min. of reaction. Fourier transform infrared spectroscopy was used to study the functional groups present in the plant biomolecules which aided the reduction and stabilization of the nanoparticles. Transmission electron microscopy analysis and X-ray diffraction pattern showed the particle sizes and crystalline structures, while the zeta potential values indicated the stability of the nanoparticles. The 5 mM concentration gave the largest particle sizes of about 12.90 nm and the most stable particles. The photocatalytic properties of the particles studied using Methyl red showed a low efficiency of 17.85% degradation achieved under 2 h. The antibacterial potency of the nanoparticles was screened against some gram-negative and gram-positive bacteria. The results showed that the nanoparticles have good antibacterial activities.