The ultralow lattice thermal conductivity, negative thermal expansion and thermoelectric properties for the face centered cubic phase of lanthanum nitride (LaN) have been explored for the first time from first-principle density functional theory and ab-initio molecular dynamics calculations. The elastic constants, phonon dispersion relations, mode Grüneisen parameter, phonon group velocity and phonon-phonon scattering rates have been studied to unveil the ultralow lattice thermal conductivity (κl = 1.08 Wm-1K-1) of the compound at room temperature (T = 300 K). The negative thermal expansion of LaN has been estimated from the mode Grüneisen parameter. The electronic band structure, hole-electron effective masses and the thermoelectric properties including the Seebeck coefficient, electrical conductivity, electronic thermal conductivity and thermoelectric power factor have been investigated to estimate the high thermoelectric figure of merit (ZT ~ 0.98) of the system at room temperature. We believe that the present study will help to unfold LaN for its applications in thermoelectric power generators, fibre-optic communications, fuel cells and in clean and global energy conservation.