This paper introduces application of genetic algorithm (GA) in designing air-termination system of the high-voltage (HV) open-air substation external lightning protection system (LPS). As far as the authors are informed, this is the first proposal for using GA in designing LPS of substations. The complex air-termination system, as a part of the external LPS of HV substation, is known to be cumbersome to design using traditional techniques, where optimisation is often relegated to the trial-and-error approach. In addition, traditional methods are often associated with geometric constraints and implementation difficulties. This paper proposes a novel approach which utilizes a combination of statistical LPS efficiency and GA in designing techno–economically optimal external LPS of open-air substations. The LPS optimisation problem is particularly well suited to the GA solution approach, due to the stochastic nature of lightning, expert knowledge involved in constructing the fitness function, and the fact that the optimal solution is not, strictly speaking, a unique value (it can be obtained using different combinations of the air-termination system elements). Proposed approach offers a LPS designer unique and valuable assistance in optimally arranging elements of air-termination system for obtaining maximum lightning shielding effects with minimum total investments.