This study investigates the excitonic dark states in single-layer tungsten disulfide (WS₂) using two-photon excitation spectroscopy. The research reveals that the strong light-matter interaction in WS₂ is dominated by excitonic effects rather than band-to-band transitions. The excitonic dark states are observed through two-photon absorption-induced luminescence (TPL), which is distinct from one-photon absorption. The excitons in WS₂ are identified as Wannier excitons with an exceptionally large binding energy of ~0.7 eV, significantly larger than that of conventional semiconductors. This large binding energy results in a quasiparticle band gap of 2.7 eV, indicating a strong many-electron effect in the 2D system. The excitonic states in WS₂ deviate significantly from hydrogen-like models, with unique energy level structures and orbital angular momentum dependencies. The excitonic energy levels are robust against environmental perturbations, demonstrating the stability of these states even at room temperature. The study also shows that the excitonic binding energy is influenced by reduced dimensionality, large effective masses, and weak dielectric screening, which are key factors in the strong light-matter interaction in 2D TMDC systems. The findings highlight the importance of many-electron effects in 2D gapped systems and open new possibilities for the application of TMDC monolayers in computing, communication, and biosensing. The results are supported by first-principles calculations using the GW-BSE method, which predict a quasiparticle band gap larger than previously reported. The experimental results align with these theoretical predictions, confirming the dominance of excitonic effects in the optical response of WS₂. The study also explores the impact of different dielectric capping layers on the excitonic energy levels, showing that the excitation energies remain robust to environmental changes. The robustness of the excitonic states suggests that the measured excitation energies are intrinsic to the monolayer, consistent with ab-initio calculations. The discovery of these excitonic dark states and their unique properties provides a foundation for further exploration of strong light-matter interactions in 2D materials.This study investigates the excitonic dark states in single-layer tungsten disulfide (WS₂) using two-photon excitation spectroscopy. The research reveals that the strong light-matter interaction in WS₂ is dominated by excitonic effects rather than band-to-band transitions. The excitonic dark states are observed through two-photon absorption-induced luminescence (TPL), which is distinct from one-photon absorption. The excitons in WS₂ are identified as Wannier excitons with an exceptionally large binding energy of ~0.7 eV, significantly larger than that of conventional semiconductors. This large binding energy results in a quasiparticle band gap of 2.7 eV, indicating a strong many-electron effect in the 2D system. The excitonic states in WS₂ deviate significantly from hydrogen-like models, with unique energy level structures and orbital angular momentum dependencies. The excitonic energy levels are robust against environmental perturbations, demonstrating the stability of these states even at room temperature. The study also shows that the excitonic binding energy is influenced by reduced dimensionality, large effective masses, and weak dielectric screening, which are key factors in the strong light-matter interaction in 2D TMDC systems. The findings highlight the importance of many-electron effects in 2D gapped systems and open new possibilities for the application of TMDC monolayers in computing, communication, and biosensing. The results are supported by first-principles calculations using the GW-BSE method, which predict a quasiparticle band gap larger than previously reported. The experimental results align with these theoretical predictions, confirming the dominance of excitonic effects in the optical response of WS₂. The study also explores the impact of different dielectric capping layers on the excitonic energy levels, showing that the excitation energies remain robust to environmental changes. The robustness of the excitonic states suggests that the measured excitation energies are intrinsic to the monolayer, consistent with ab-initio calculations. The discovery of these excitonic dark states and their unique properties provides a foundation for further exploration of strong light-matter interactions in 2D materials.