A novel low-cost titanium alloy Ti₈₆Al₉Fe₂Mo₃ was designed based on the d-electron theory. The evolutionary relationships between microstructure and mechanical properties of the alloy under different aging temperatures (700 °C, 740 °C, and 820 °C) were investigated. The results show that with the increase of aging temperature, the content of β phase gradually increases while that of α phase decreases, and the size of β phase tends to decrease with a more uniform distribution. Temperature, the content of β phase gradually increases while that of α phase decreases, and the size of β phase tends to decrease with a more uniform distribution. Among the tested conditions, the alloy aged at 700 °C exhibits the optimal comprehensive mechanical properties, with a tensile strength of 2160 MPa and an elongation of 42%, which are 42.01% and 61.5% higher than those of the as-cast alloy, respectively. Additionally, as the heat treatment temperature increases, the fracture mode of the alloy transforms from brittle fracture to ductile fracture.