This study aims to examine the intervening construct of role ambiguity on the causal association between leadership and organisational citizenship behaviour (OCB) in various industrial settings. The sample of this study involved 280 respondents from major industries i.e. services, manufacturing, mining and construction. The results of the Pearson correlation analysis indicate that a transformational leader has a positive relationship with OCB and that a transactional leader has a negative relationship with OCB. Role ambiguity was found to mediate the causal relationship between a transformational leader and OCB. Role ambiguity is not directly linked to OCB but rather serves as a mediating variable between transformational leadership style and OCB. From a managerial standpoint, this study recommends that transformational leadership style should be emphasised to encourage greater OCB. Cultivating transformationally-orientated organisation at all levels can be done through training and development, organisational design, job design and human capital decisions. The mediating effect of subordinates' role ambiguity has a direct and indirect effect on OCB. Role ambiguity functions to increase the strength of transformational leadership on OCB. These findings show that the effectiveness of leadership styles is mediated by subordinates' perception of their role ambiguity. This paper adds value to existing study in this field by testing the mediating effects of role ambiguity that directly or indirectly affect leadership styles related to OCB.