<p>In this work, we systematically studied the electronic and optical properties of monolayer GaTe (GaTe-1L) using first-principles calculations. The electronic characteristics are explored at various levels of theory, including density functional theory (DFT), DFT + spin–orbit coupling (SOC), Heyd–Scuseria–Ernzerhof (HSE), and GW standards, revealing key features such as electronic band structures, Van Hove singularities in the density of states, charge density distributions, and differences. By examining the dielectric function, absorption, reflectance, and energy loss spectra, the impacts of electron–electron and electron–hole interactions on the optical response are elucidated, highlighting strong excitonic effects, several single-particle excitation features, and distinct plasmon resonances. Furthermore, distinct correlations are established among the vertical electronic transitions in the band structures, the orbital-resolved contributions to DOS, and the prominent features in the imaginary part of the dielectric function, considering electron–electron interactions. These results provide valuable insights into the potential of GaTe-1L for applications in electronic and optoelectronic devices. The theoretical approach adopted here can be readily extended to other graphene-like and emerging two-dimensional materials.</p>