Abstract: Two-dimensional SnSe monolayers have an excellent prospect in thermoelectric applications. We investigated the structure, electron and phonon properties of 2D monolayer SnSe doped with 1D Mn nanowires using the first principle calculation within density functional theory. This directional doping is totally different from the existing random doping methods. The Boltzmann theory for electrons under relaxation time approximation was employed to obtain the Seebeck coefficient and electrical conductivity. The lattice thermal conductivity was calculated using the Boltzmann Transport Equation method and the Debye-Callaway model. The results show that the doping of 1D Mn nanowires can enhance the phonon scattering process by introducing wire defects, and reduce the lattice thermal conductivity. By adjusting the width between nanowires, record high ZT values from 0.71 at 200 K to 3.76 at 650 K are achieved, 37.8% larger than the intrinsic monolayer SnSe on average.