Temperature-insensitive elastic modulus known as Elinvar effect is typically achievable in metastable titanium alloys only through thermomechanical processing. Here reports that a directly additively manufactured TiNb-based alloy exhibits Elinvar effect over a wide temperature range of 273 K. This is attributed to its α″+β dual-phase microstructure wherein both the elastic modulus and transition strain of the α″ phase increase monotonically with increasing temperature. The α″ phase was obtained by setting a base-plate temperature of 723 K to act as in-situ aging. This provides a new way to optimize mechanical and functional properties simultaneously by utilizing thermal fields of additive manufacturing.