This study presents first-principles calculations of the optical response of monolayer molybdenum disulfide (MoS₂) using the GW-Bethe Salpeter equation (GW-BSE) approach, which includes self-energy, excitonic, and electron-phonon effects. The results show that monolayer MoS₂ has a large number of strongly bound excitonic states with novel k-space characteristics not previously observed. The absorption spectrum is dominated by excitonic states with binding energy close to 1 eV and is broadened by electron-phonon interactions in the visible to ultraviolet range. These findings resolve inconsistencies in previous GW-BSE calculations and explain recent experimental measurements. Monolayer MoS₂, a two-dimensional material, has a direct band gap at the K and K' points in the Brillouin zone due to inversion symmetry breaking. It exhibits strong excitonic effects, which influence its optical properties. The GW-BSE method is used to compute quasiparticle band structure and optical response, including electron-electron interactions and excitonic contributions. However, previous GW calculations of MoS₂ have reported conflicting findings, with some concluding a direct gap and others an indirect gap. The study shows that the GW-BSE formalism is not the issue, but rather the computational complexity of MoS₂. A large number of bands and a high energy cutoff are required for accurate calculations. The study finds that MoS₂ has a large number of excitonic states with diverse characteristics, which are necessary for understanding experimental absorption spectra and recent time-resolved photoluminescence spectra. The study calculates the quasiparticle band structure and optical spectrum of MoS₂ from first principles, achieving convergence within 0.1 eV. The absorption spectrum is found to have rich additional physics between the energies of the first two bound exciton states and the quasiparticle gap. The study identifies multiple excited states of the first set of bound excitons and their respective intra-exciton transition energies. These new states are necessary for a conceptual and quantitative understanding of experimental absorption spectra. The study also shows that the apparent discrepancy between calculated and experimental absorption spectra is due to electron-phonon interactions, which are accounted for in the calculations. The results suggest that variations in temperature, dielectric screening, and mechanical strain could affect the optical absorption in this region of the spectrum. The predicted features associated with higher energy excitonic states may be enhanced and observed in experiments at reduced temperatures or through modulation techniques. The large number and diverse character of excitons in the energy window between 2.2 and 2.8 eV suggest that MoS₂ is an ideal system for studying inter- and intra-exciton transitions.This study presents first-principles calculations of the optical response of monolayer molybdenum disulfide (MoS₂) using the GW-Bethe Salpeter equation (GW-BSE) approach, which includes self-energy, excitonic, and electron-phonon effects. The results show that monolayer MoS₂ has a large number of strongly bound excitonic states with novel k-space characteristics not previously observed. The absorption spectrum is dominated by excitonic states with binding energy close to 1 eV and is broadened by electron-phonon interactions in the visible to ultraviolet range. These findings resolve inconsistencies in previous GW-BSE calculations and explain recent experimental measurements. Monolayer MoS₂, a two-dimensional material, has a direct band gap at the K and K' points in the Brillouin zone due to inversion symmetry breaking. It exhibits strong excitonic effects, which influence its optical properties. The GW-BSE method is used to compute quasiparticle band structure and optical response, including electron-electron interactions and excitonic contributions. However, previous GW calculations of MoS₂ have reported conflicting findings, with some concluding a direct gap and others an indirect gap. The study shows that the GW-BSE formalism is not the issue, but rather the computational complexity of MoS₂. A large number of bands and a high energy cutoff are required for accurate calculations. The study finds that MoS₂ has a large number of excitonic states with diverse characteristics, which are necessary for understanding experimental absorption spectra and recent time-resolved photoluminescence spectra. The study calculates the quasiparticle band structure and optical spectrum of MoS₂ from first principles, achieving convergence within 0.1 eV. The absorption spectrum is found to have rich additional physics between the energies of the first two bound exciton states and the quasiparticle gap. The study identifies multiple excited states of the first set of bound excitons and their respective intra-exciton transition energies. These new states are necessary for a conceptual and quantitative understanding of experimental absorption spectra. The study also shows that the apparent discrepancy between calculated and experimental absorption spectra is due to electron-phonon interactions, which are accounted for in the calculations. The results suggest that variations in temperature, dielectric screening, and mechanical strain could affect the optical absorption in this region of the spectrum. The predicted features associated with higher energy excitonic states may be enhanced and observed in experiments at reduced temperatures or through modulation techniques. The large number and diverse character of excitons in the energy window between 2.2 and 2.8 eV suggest that MoS₂ is an ideal system for studying inter- and intra-exciton transitions.