The optical properties of $\mathrm{Ag}\mathrm{Ga}{\mathrm{Te}}_2$ chalcopyrite semiconductor are studied by optical absorption, spectroscopic ellipsometry (SE), and thermoreflectance (TR) spectroscopy. Optical absorption spectra suggest that $\mathrm{Ag}\mathrm{Ga}{\mathrm{Te}}_2$ is a direct-gap semiconductor having a bandgap of $\sim 1.2\mathrm{eV}$ at $T=300\mathrm{K}$ . The pseudodielectric-function spectra of $\mathrm{Ag}\mathrm{Ga}{\mathrm{Te}}_2$ are determined by SE in the range between $E=1.2$ and $5.2\mathrm{eV}$ for both states of polarization. These spectra reveal distinct structures at energies of the critical points in the Brillouin zone. The TR spectra are also measured in the $E=1.0–5.3\mathrm{eV}$ ranges at $T=20\mathrm{K}–300\mathrm{K}$ . The spin–orbit and crystal-field splitting parameters of $\mathrm{Ag}\mathrm{Ga}{\mathrm{Te}}_2$ are determined to be ${\mathrm{\Delta }}_{\text{so}}=0.70\mathrm{eV}$ and ${\mathrm{\Delta }}_{\text{cr}}=-0.23\mathrm{eV}$ , respectively.