Double perovskite halides are emerging as promising materials for renewable energy applications, offering key properties such as tunable photoelectric characteristics and high stability, which make them strong candidates to help combat global energy shortages. In this work, we investigated the structural, electronic, and optical properties of the lead-free double perovskite \(\mathrm {Cs_2AgIrBr_6}\) using first-principles calculations based on Density Functional Theory (DFT) within the Generalized Gradient Approximation (GGA). The optimized geometry confirms the structural stability of the compound, as further supported by the analysis of geometric tolerance factors. The electronic band structure shows an indirect band gap of 0.56 eV (L \(\rightarrow \Gamma \) ), while the density of states analysis highlights significant contributions from Ir-d and Br-p orbitals. Optical analysis demonstrates strong absorption in the visible and ultraviolet ranges, with high absorption coefficients up to \(\mathrm {1.8 \times 10^6\,cm^{-1}}\) and a Tauc-derived optical band gap of 1.97 eV. These findings confirm that \(\mathrm {Cs_2AgIrBr_6}\) is a promising candidate for optoelectronic applications, especially in infrared photodetectors and tandem solar cells.