Radio frequency (RF) spectrum is already dense enough and hard to add more broadband channels to meet the current user demands. Optical free-space communications could be an excellent alternative to the RF communications system, and it provides additional benefits, e.g., large bandwidth, high data rates and reliable communication link. Therefore, free-space optical (FSO) communication system becomes more attractive for the deployment of additional broadband channels, and it fulfils the current user demands of bandwidth-hungry applications. FSO communication links are susceptible to numerous meteorological conditions such as fog, snow, dust, smoke, scintillation and smog. Achieving better connectivity under the above-mentioned severe conditions is a crucial research question. Joint optical-RF communication system is developed to overcome the problems as mentioned earlier. The proposed adaptive optical-RF transmission system is optimized so that the system performance is maximized under all channel conditions. Optimization is achieved over the respective channel mappings, and the total required power by exploiting the proposed algorithm. The mapping schemes of each link are optimally chosen such that the total mutual information is maximized while distributing optimal power to the individual channel. Simulations are performed and verified with the analytical results to validate the proposed design. A comparison of the adaptive joint system (i.e., hybrid FSO-RF) over the non-adaptive system under various weather conditions is provided. From simulation results, the performance gain of more than 1 dB is achieved under the minimum power level. It is, therefore, recommended that the adaptive hybrid FSO-RF communication system is always an optimum solution for all weather conditions.