The high energy consumption of office buildings, particularly in hot and dry climates, has increased the necessity of employing passive strategies to control environmental conditions and reduce cooling loads. One of the most effective solutions in this regard is the use of external shading devices, such as louvers, to control solar radiation and improve building energy performance. The present study aimed to determine the optimal angle of external louvers and evaluate their effect on the energy consumption of an office building in the hot and dry climate of Kerman. For this purpose, an office building was simulated as a base-case model in DesignBuilder software, and its energy performance was examined with horizontal and vertical louvers installed on the south and west façades. Various louver angles—0°, 10°, 20°, 30°, 40°, 50°, and 60°—were analyzed across 21 independent simulation scenarios. The evaluation indicators included incident solar radiation, cooling load, heating load, lighting energy consumption, and total building energy consumption. The results showed that increasing the louver angle reduces incident solar radiation and cooling load; however, at larger angles, lighting energy consumption increases due to reduced daylight availability. Horizontal louvers were also found to be more effective than vertical louvers in reducing overall energy consumption. Based on the results, a horizontal louver with a 30° angle on the south façade and a horizontal louver with a 40° angle on the west façade were introduced as the optimal options in terms of total energy consumption. The findings of this study can be applied to the envelope design of office buildings in hot and dry climates and to the development of sustainable architectural strategies.