Background Loneliness threatens mental and physical health. While previous research has identified various social and demographic correlates, there is limited knowledge of how individual differences relate to loneliness severity and persistence. This study investigates the role of self-efficacy and personality traits, including their relevance for differentiating between transient and chronic loneliness. Methods Data from two studies were analyzed: a representative German population survey ( N = 2527) and an Austrian-German online sample ( N = 553). Loneliness was assessed using the UCLA 3-item Loneliness Scale, and chronic loneliness was defined based on reported duration. Self-efficacy was measured using the German ASKU (Allgemeine Selbstwirksamkeit Kurzskala). Personality traits were assessed with the Big Five Inventory (BFI-10). Correlational analyses, regression models, and multinomial logistic regressions were used to examine associations between individual differences and loneliness. Results Lower self-efficacy was associated with higher loneliness across both studies. Chronically lonely individuals reported lower self-efficacy than those with temporary loneliness. Among the Big Five traits, higher neuroticism and lower extraversion showed the strongest associations with current loneliness, and there were interaction effects with openness. Conclusions The findings highlight self-efficacy as a potential protective factor against loneliness. Interventions aimed at strengthening self-efficacy could help mitigate long-term loneliness.