The poor strength-ductility balance of Mg alloys at room temperature restricts their application and development. Texture engineering and grain boundary design are critical strategies for optimizing their mechanical properties. In this study, a high-strength-ductility binary Mg-7Sn alloy was fabricated through a composite processing route involving warm extrusion followed by room-temperature rolling. During the composite processing, a bimodal grain structure featuring dual-texture characteristics and a high proportion (38%) of low-angle grain boundaries (LAGBs) was formed in the alloy. The formation of a dual-texture microstructure, which consisted of C-texture (<0001>//RD) and basal texture, effectively weakened the intensity of the basal texture. Tensile test results indicated excellent strength-ductility balance, with yield strength, ultimate tensile strength, and elongation to failure being 235.6 MPa, 315.7 MPa, and 16.8%, respectively. The improvement in yield strength was primarily attributed to grain boundary strengthening, whereas the excellent ductility can be attributed to the enhanced crack initiation resistance and crack deflection enabled by the dual-texture structure, as well as the favorable local strain compatibility arising from the high volume fraction of LAGBs. This study provides valuable insights into the development of high-performance Mg alloys via texture engineering and grain boundary design.