The development of one-dimensional (1D) molecular nanowires with high spin-polarization is important for both fundamental research and practical applications in nanoscale spintronics. Herein, we report new 1D metal trihydride molecular nanowires MH3 (M = Sc, Cr, Mn, and Co) with versatile magnetic properties on the basis of first-principles calculations and molecular assembly of their molecular motifs. Among the 1D nanowires considered, CrH3, MnH3, and CoH3 are either antiferromagnetic or ferromagnetic in their ground states. In particular, CoH3 nanowire is a half-metal, which ideally could provide 100% spin-polarized currents. Moreover, carrier doping in MnH3 nanowire can induce a transition from ferromagnetic metal to half-metal. Strong metal metal interaction in 1D MH3 nanowires is responsible to versatile magnetic properties and high Curie temperature. Born-Oppenheimer molecular dynamics simulation indicates that these nanowires are stable at elevated temperature. In particular, the ScH3 nanowire appears to have the highest structural stability at temperature 1200 K. These novel properties of 1D MH3 nanowires render their potential applications in nanoscale spintronics.