The concept of the smart city is well-established, and governments across the world are either planning, or already implementing, strategies to transform existing cities to smart status. However, governments cannot act alone. If the implementation of these smart city strategies are to be successful, public engagement is a key factor. This raises the question of how best to ensure public engagement. Currently, the various external factors that influence willingness to support, and actively participate in, the development of smart cities are not well-understood, as there are few studies which examine the issue. This is of significance across the globe, but is of particular significance in Saudi Arabia, which has announced an ambitious smart city development plan. The aim of this research is to explore this issue—that is, it seeks to identify the key variables that influence the intention to participate in smart city development, and explores how they ultimately affect engagement behaviours. To achieve this, the study used a quantitative methodology, based on data from residents of 10 Saudi cities, each of which is part of the Kingdom’s 2030 smart city plan. The data were analysed, using structural equation modelling (SEM), in order to test the reliability and predictive value of a model which hypothesised a positive relationship between five external variables: information availability, perceived benefits, social norms, behaviour management, and social responsibility and engagement behaviour. The results showed that information availability has a direct and positive effect on an individual’s engagement behaviour, while perceived benefits, responsibility and social norms have an indirect effect on engagement, by positively impacting the attitude of residents. Practical implications, based on these findings, are discussed. The study contributes important insights to the literature, as it is one of the few studies to explore such a model in the context of smart cities. It therefore acts as a useful foundation for further research. However, the focus on Saudi cities may be considered a limitation in terms of generalisability, and other external variables could usefully be explored in future research.