Social skills are the basis of human interactions and functioning in society. Social competence (SC) is thought to evolve gradually during childhood and adolescence via the interplay of multiple factors. In particular, the early years of life are marked by the emergence of basic social abilities and constitute the foundation for successful social development. The biopsychosocial SOcio-Cognitive Integration of Abilities modeL (SOCIAL) posits that internal (child-based), external (environment), and cognitive factors are critical to SC in the context of normal brain maturation; but this has yet to be shown empirically and comprehensively. This study tested the SOCIAL model in a sample of typically developing preschool children. Parents of 103 children (M = 67.59 months, SD = 11.65) completed questionnaires and children underwent neuropsychological assessment of executive functioning (EF), communication skills and social cognition. Three-step hierarchical regression analyses (1) Internal factors, 2) External factors, 3) Cognitive factors) confirmed that each step of the regression model significantly predicted SC. In the final model, general cognitive and socio-cognitive factors significantly predicted SC above and beyond internal and external factors: children with lower temperamental negative affect and less parent-reported executive dysfunction, as well as better non-verbal communication and theory of mind had better SC. Our findings support the conceptual SOCIAL model, and highlight the importance of internal, external, and cognitive factors for SC in the preschool years. Identification of factors associated with early social development can inform both normative and clinical approaches to identifying intervention loci and optimizing SC in those at risk for maladaptive social functioning.