Shisha smoking has increased significantly worldwide over the past decade including in developing countries such as Nigeria. We aimed to understand the reasons for shisha smoking in Nigeria in order to address the lack of context-specific evidence to inform the national response to the growing threat posed by shisha smoking. We adopted the Theory of Planned Behaviour to conduct in-depth interviews among 78 purposely sampled current shisha smokers in 13 states (six in each state), and a quantitative survey including a random sample of 611 current shisha smokers in 12 states, across the six geopolitical zones in Nigeria. The in-depth interview data was analysed using thematic analysis whilst the quantitative survey data was analysed descriptively. We triangulated the key findings from the two datasets using a triangulation matrix organised by the three meta-themes: attitude, subjective norms, perceived behavioural control. Positive attitudes towards shisha smoking stem from shisha flavours, perceived pleasure from shisha smoking, curiosity about product attributes, beliefs about health benefits, limited knowledge on the health effects, and weak regulation. Having friends and family members who smoke shisha and the need to belong, particularly during social events, also promote shisha smoking. Negative societal views towards shisha smoking are potentially a protective factor. The availability of and ability to smoke shisha in many places makes shisha more accessible, whilst the high costs of shisha are potentially prohibitive. The findings also indicate that quitting shisha smoking without support is difficult. Restrictions on flavours, strengthening compliance monitoring and enforcement of the tobacco control laws in relation to shisha (e.g., smoke-free environments in indoor and outdoor public places; health warnings in English on shisha products including the pots; and tax and price measures) have the potential to minimise initiation and use, and to protect the health and wellbeing of Nigeria’s general public.