The façade, as the exterior cladding of a building, is an essential element which provides waterproofing, thermal isolation and structural resistance against environmental actions. The vertical members in curtain wall façade systems, referred to as mullions, are the dominant load-bearing structural members. Despite aluminium being a durable material, conventional aluminium façade frames are weak in thermal performance, and hence thermal breaks are often used in the industry to provide the required insulation. In addition, timber frames may be preferred by building designers due to their aesthetic appearance and sustainability. Therefore, an innovative composite mullion was developed using aluminium and timber to combine the best features of both materials and is presented in this study. Experimental studies were also conducted to verify the structural performance of the composite mullion. The first series of tests was performed to investigate various aluminium-timber connections to ensure composite action. Four different connection types were considered in this study and the optimum connection was chosen and discussed. Four-point bending tests were performed next to investigate the bending behaviour and strength of the newly developed mullion as well as traditional aluminium mullions under positive and negative wind loading scenarios. It was found that the new composite mullions achieved higher section moment capacities than the traditional aluminium mullions, while being energy-efficient, aesthetically pleasing and more sustainable.