A heterogeneous structure composed of elongated primary α and secondary α grains with a size of 670 nm was produced by subjecting the bimodal microstructure of a titanium alloy to hot rolling, annealing, and aging treatments. This heterogeneous structure exhibited significantly improved strength owing to a combination of heterogeneous deformation-induced strengthening and dislocation strengthening. A short-duration high-temperature heat treatment facilitated a synergistic enhancement of yield strength and elongation at both room temperature and 650 °C. The fracture elongation at room temperature and 650 °C increased by 36.7% and 130.4%, respectively, compared with that of bimodal microstructure. The stacking of geometrically necessary dislocations with a single slip system at the phase boundary and the longer effective slip length of the dislocations are the reasons for the significant improvement in elongation. The elongated primary α phase in lamellar bimodal microstructure, composed of multiple primary α grains, has better resistance to the anti-fatigue crack initiation effect.