The current study focuses on understanding the factors (subjective norms (SNs), personal attitude, and perceived behaviour control (PBC)) that influence consumer purchase intention regarding organic food from the theory of planned behaviour and health consciousness as an additional factor in Tanzania and Kenya. It further explains the role of knowledge as a moderating variable in organic food purchase intention. A total of 331 responses from Tanzania and 350 responses from Kenya were obtained. Confirmatory factor analysis was applied for validation, and results were analysed using structural equation modeling. SNs, personal attitudes, and health consciousness were found to be significant predictors of organic purchase intention in both countries. Furthermore, findings show that knowledge positively moderates the relationship among SNs, personal attitude, health consciousness, and organic food purchase intention. However, PBC was found to be a weak influencer on consumer purchase intention in Kenya, and no knowledge interaction between PBC and consumer purchase intention in Tanzania was found. The current study theoretically contributes to the literature by introducing the moderating role of knowledge in the relationship. The results show that knowledge interaction increases the effects of the majority of predictors after being introduced in the relationship. Finally, this study provides an understanding of consumers’ perspective regarding their intention to purchase organic foods, which will help stakeholders, such as marketers, retailers, and producers, to achieve marketing strategies for the development of these products.