Background Based on propositions of the contextual model of parenting style, we examined whether there is a relationship between parent-youth sexual risk communication (PYSRC) and premarital sexual debut, and whether this relationship is moderated by the parenting style. Methods A cross-sectional study design was employed, and data were collected using a self-reported questionnaire from 462 youth (211 boys and 251 girls) aged 15–24 years in senior grades of three public high schools (two rural and one urban) in Eswatini (formerly Swaziland). A hierarchical binary regression analysis was conducted to examine the association between PYSRC and premarital sexual debut, and to test whether parenting style moderates this relationship. Results The mean age of participants was 18.9 (±1.85) years, and a slight majority were females (54.3%). About 35.9% of participants reported having had sex (i.e., premarital sexual debut). After adjusting for age, gender, living arrangement, school location, and peer sexual activity, neither PYSRC (adjusted odds ratio [AOR] = 1.01, 95% confidence interval [CI]: 1.00, 1.03) nor parenting style (AOR = 0.81, 95% CI: 0.64, 1.04) significantly predicted premarital sexual debut in the sample. Likewise, parenting style did not significantly moderate the relationship between PYSRC and premarital sexual debut (AOR = 1.01, 95% CI: 1.00, 1.02). Conclusion Contrary to propositions of the contextual model of parenting style, in this study, parenting style (authoritativeness) did not moderate the studied relationship, indicating the need for more studies to test the applicability of the contextual model of parenting style in African settings.