Valley degrees of freedom in two-dimensional (2D) materials promise revolutionary advances in information processing, yet their practical implementation faces fundamental challenges. While hexagonal transition-metal dichalcogenides require external fields to break valley degeneracy, anisotropic materials such as tin sulfide (SnS) offer intrinsically nondegenerate valleys addressable with linearly polarized light—but understanding valley-specific dynamics remains elusive. Here, we demonstrate that resonant Raman scattering unveils a direct fingerprint of valley identity through strong reorganization of exciton-phonon coupling. At the $X_1$ valley (1.37 eV), the $A_g^3$ breathing mode dominates with fourfold enhancement over $A_g^4$, while this hierarchy completely inverts at the $X_3$ valley (1.68 eV) where $A_g^4$ shows sixfold stronger coupling. This valley-specific coupling originates from the distinct orbital characters, as revealed by our density functional theory calculations: $p_x$ orbitals at $X_1$ couple efficiently to symmetric breathing motions, whose symmetric compression/extension modulates the $p_x\text{−}{p}_x$ overlap. Conversely, the mixed $s\text{−}p$ orbitals at $X_3$ favor complex displacement patterns. Beyond conventional Raman modes, we observe resonant activation of infrared-active phonons through Fröhlich coupling, with valley-dependent polarization selection rules and activation energies of 4.6–13.2 meV. Power-dependent measurements reveal valley-specific saturation behaviors, with $X_3$ saturating at three times lower carrier densities than $X_1$ due to differences in band curvature. These findings establish phonon scattering as an intrinsic probe of valley physics, enabling optical identification and potentially manipulation of valley states. Our results demonstrate that exciton-phonon coupling in anisotropic 2D materials fundamentally encodes valley information, opening pathways for phonon-mediated valley control in next-generation valleytronic devices.

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• Excitons
• Phonons
• Layered crystals
• Band structure methods
• Luminescence
• Raman spectroscopy