Ternary layered nitrides have received widespread attention due to their unique electrical, optical and optoelectronic properties, which are promising for the fabrication of low-cost and high-efficiency optoelectronic materials, solar cell materials and photocatalysts. Although there is a lack of experimental reports on BaTiN₂ so far, BaZrN₂ and BaHfN₂ have been synthesized experimentally by solid state methods. However, their optical and electrical transport properties have not been investigated systematically. This work is to systematically investigates the mechanical, electronic, optical absorption, carrier transport, and dielectric response properties of BaMN₂ (M = Ti, Zr, Hf) nitrides through first-principles calculations based on density functional theory. Due to the quasi-two-dimensional layered arrangement of MN₂^2– slabs, the ionic bonds between Ba²⁺ and N^3–, and the weak interactions between the slabs, the deformation along this direction is most likely to occur under the action of external stress. BaMN₂ nitrides exhibit significant anisotropic physical properties. Firstly, the mechanical properties of BaMN₂, such as bulk modulus, shear modulus, Young’s modulus, and Poisson’s ratio, show prominent anisotropy. The lower modulus, higher Poisson’s ratios and Pugh’s modulus ratios indicate good flexibility of the BaMN₂ nitrides. In addition, BaMN₂ has indirect bandgap values (1.75–2.25 eV) within the visible-light energy range, which meets the basic requirement for the band gap of a photocatalyst for water splitting (greater than 1.23 eV). Moreover, BaMN₂ has suitable band-edge positions. The appropriate bandgap values and band-edge positions indicate their broad application prospects in the absorber layer of solar cells and photocatalytic water decomposition. Due to the significant difference in the effective mass of its charge carriers between different directions, BaMN₂ exhibits ultrahigh anisotropic carrier mobility (on the order of 10³ cm²⋅s^–1⋅v^–1) and lower exciton binding energy. At the same time, there are significant differences in atomic arrangement and bonding interactions between the in-plane direction and out of plane direction, resulting in high anisotropic visible-light absorption coefficient (on the order of 10⁵ cm^–1) in the low energy region. In contrast, the increase of the opportunity for electrons to transition from occupied to unoccupied states leads to more complex light absorption and relatively reduced anisotropy in higher energy region. Furthermore, the special layered structure has lower polarizability and higher vibration frequency along the vertical direction perpendicular to the MN₂^2– layers, rendering BaMN₂ nitrides show high dielectric constants. These excellent anisotropic mechanical, optoelectronic, and transport properties allow BaMN₂ layered nitrides to be used as promising semiconductor materials in the fields of optoelectronics, photovoltaics, and photocatalysis.