There are growing concerns that seem to suggest that students no longer engage in school-related activities as they ought to. Recent observation has revealed that students now spend excessive time participating in Internet gambling with their smartphone during school period. This trend could have far-reaching consequences on their schoolwork engagement and by extension, academic performance. Drawing on the Dualistic Model of Passion, this study therefore, examined the mediatory role of smartphone addiction in the gambling passion—schoolwork engagement relation. A cross-sectional design was adopted. Male undergraduates (N = 278) of a large public university in Nigeria who engage in Internet gambling participated in the study. They completed self-report measures of gambling passion, smartphone addiction, and schoolwork engagement. Results showed that harmonious gambling passion was not related to smartphone addiction whereas it was positively related to schoolwork engagement. Obsessive gambling passion had positive and negative relations with smartphone addiction and schoolwork engagement, respectively. Smartphone addiction was negatively related to schoolwork engagement and mediated only the obsessive gambling passion—schoolwork engagement relation but not that between harmonious gambling passion and schoolwork engagement. The theoretical and practical implications of the findings are discussed.