Sustainable urban mobility paradigm has recently gained prominence in both developed and developing cities, yet the transition process raises important concerns and issues. Socio-technical transition perspective provides a useful way to interpret the social and technical dynamics and complexities involved in sustainability transitions. However, the context of developing megacities presents significant differences with that of the developed cities in terms of institutional settings, governance structures, and urban mobility challenges. This paper proposes a socio-technical transition perspective to examine and analyze the urban mobility systems in developing mega cities. In addition, a multi-level perspective is offered to understand the dynamics of sustainable urban mobility transitions. The case study of Istanbul, a developing megacity having a population of nearly 15 million people with many urban mobility problems such as chronic traffic congestion, overcrowded public buses, traffic accidents and injuries, air and noise pollution, helps substantiate the proposed socio-technical perspective. The theoretical insights and empirical findings strongly suggest the potential usefulness of this perspective for other megacities grappling with similar problems.