High-mobility p-type semiconductors are essential for advanced electronic devices but remain scarce. Here, using a hierarchical screening framework that combines first-principles calculations with Boltzmann transport theory, we identify MN₂ (M= Mo and W) family as polar semiconductors with exceptionally high intrinsic hole mobilities. In particular, 1H-WN₂ exhibits a room-temperature hole mobility exceeding 10⁴~cm² V⁻¹ s⁻¹. This exceptional transport performance arises from the synergistic suppression of polar-optical-phonon and acoustic-phonon scattering, together with a reduced intervalley-scattering phase space induced by spin–valley locking. These effects arise from anomalously small Born effective charges, strong covalent N–N bonds, and orbital hybridization between N-2pₓ/2p_y and W-5d_xy/5d_(x²-y²) in the N₂-dimer-based structure. Our results establish MoN₂ and WN₂ as a promising class of high-mobility polar semiconductors and introduce a crystal-structure-based strategy for concurrently suppressing multiple electron–phonon scattering channels, thereby revising design principles for high-mobility materials.