This work presents a first-principles study of the structural and electronic properties of (Ge₂)₁₋ₓ(InP)ₓ solid solutions across the full composition range (0 ≤ x ≤ 1). Calculations were performed within density functional theory using the all-electron FHI-aims code, with r2SCAN for structural optimization and HSE06 for accurate band gap evaluation, including spin–orbit coupling effects. The results show that lattice parameters increase with composition following Vegard’s law. The band structure exhibits strong composition dependence, with band gap reduction and eventual band overlap at intermediate concentrations (x ≈ 0.5). These effects are attributed to electronic state hybridization. The findings highlight the potential of these alloys for tunable optoelectronic applications.