We investigate the effects of Bi substitution on the structure, magnetization, magnetoresistance, and magnetostrain in single crystals of (MnSb)Bi (x = 0.06, 0.08, 0.1, and 0.12). It is found that the element Bi can be partially substituted for Sb in the tetragonal MnSb main phase, and partially forms the MnBi and Bi-rich secondary phases. The introduction of Bi causes the simultaneous lattice shrinkages in a and c for the main phase, and also enhances the transition temperature of the first-order magnetoelastic ferrimagnetic-antiferromagnetic transition. Such an enhancement in transition temperature due to contraction of the unit-cell volume contraction is also experimentally proven based on the thermomagnetic curves under hydrostatic pressure for a crystal with × = 0.12. The volume contraction rate due to hydrostatic pressure is deduced to be −0.0386 Å/GPa. Moreover, the highest values of in-plane magnetoresistance (∼-30%) and magnetostrain (∼−1448 ppm) with good reversibility are attained at 120 K under 30 kOe, which was proven to be the optimal magnetic field. Our experimental results show that MnSb-based intermetallic compounds can be considered promising candidates for low-cost, multifunctional magnetic materials.