Temperature-dependent single-crystal elastic stiffness constants and the associated polycrystalline aggregate properties of fcc-based metal nitrides (MNs; M = Ti, Al, Zr, and Hf) have been investigated using a quasistatic approach via first-principles calculations. It is confirmed that the four studied nitrides are brittle materials and mechanically stable, agreeing with experimental results. Among these compounds, TiN and AlN possess the highest strength and the highest hardness, respectively. The cross-slip and the resistance to microcracks are analyzed based on the elastic anisotropy ratio. Additionally, it is found that the decreasing trend of C-11 with respect to temperature is larger than that of C-12 or C-44. With increasing temperature, the resistance of shear deformation, stiffness, hardness, and strength of these four nitrides decrease. The computed properties of MNs agree well with the experimental data available in the literature.