This study explored a novel intermetallic composite design concept based on the principle of lattice strain matching enabled by the collective atomic load transfer. It investigated the hard-soft microscopic deformation behavior of a Ti3Sn/TiNi eutectic hard-soft dual phase composite by means of in situ synchrotron high-energy X-ray diffraction (HE-XRD) during compression. The composite provides a unique micromechanical system with distinctive deformation behaviors and mechanisms from the two components, with the soft TiNi matrix deforming in full compliance via martensite variant reorientation and the hard Ti3Sn lamellae deforming predominantly by rigid body rotation, producing a crystallographic texture for the TiNi matrix and a preferred alignment for the Ti3Sn lamellae. HE-XRD reveals continued martensite variant reorientation during plastic deformation well beyond the stress plateau of TiNi. The hard and brittle Ti3Sn is also found to produce an exceptionally large elastic strain of 1.95% in the composite. This is attributed to the effect of lattice strain matching between the transformation lattice distortion of the TiNi matrix and the elastic strain of Ti3Sn lamellae. With such unique micromechanic characteristics, the composite exhibits high strength and large ductility.