Angular leaf spot disease, which is caused by the fungus Pseudocercospora griseola, is among the most damaging diseases affecting common bean (Phaseolus vulgaris L.), impacting both yield and grain quality. Because of the environmental risks associated with fungicides and the variability in the virulence of P. griseola isolates, biological control emerges as a promising alternative for managing this disease. This study assessed the biological control potential of Trichoderma asperellum 659-7, PR11, and PR12 against P. griseola. Additionally, changes in some biochemical parameters were also investigated. The findings revealed that the three tested strains stopped the growth of P. griseola during the confrontation test, achieving 100% inhibition. Furthermore, the cell-free culture filtrates from each T. asperellum strain hindered the mycelial growth and spore germination of P. griseola, with the level of inhibition depending on both the concentration of culture filtrate and the specific strain of T. asperellum. The most significant reduction was noted with T. asperellum PR11, which decreased mycelial growth by 26.33% and spore germination by 27.14% at 25% (v/v). Moreover, treating infected bean leaves with T. asperellum PR11 led to a reduction in disease severity by 11.32 and 22.5% at 14 and 21 days after inoculation, respectively. An increase in chlorophyll content (287.087%), total phenols (43.116%), and flavonoids (72.010%) was also observed when infected leaves were treated with T. asperellum PR11. These overall results endorse the effectiveness of Trichoderma asperellum PR11 as a biological control agent for managing bean angular leaf spot, offering an alternative and environmentally friendly strategy.