Background: Social network, loneliness, generalized anxiety disorder (GAD) and major depression disorder (MDD) are interrelated. However, as the directions of these associations are still unclear, we examined them prospectively using community-based data. Methods: Data on 5066 adults aged ≥ 50 years from the Irish Longitudinal Study on Ageing (TILDA) were analyzed. Loneliness was assessed through the UCLA Loneliness Scale. Social integration was measured using the Berkman-Syme Social Network Index. MDD and GAD were assessed with the Composite International Diagnostic Interview (CIDI). Logistic regression models were conducted. Results: The longitudinal association between experiencing loneliness and higher likelihood of suffering from MDD or GAD two years later is bidirectional but stronger with loneliness as origin, whereas the association between social isolation and higher likelihood of subsequent MDD or GAD as well as those between loneliness and subsequent deterioration of social integration are unidirectional. Conclusion: Objective and perceived social isolation independently affect the probability of suffering from MDD or GAD whereas loneliness is a risk factor for the deterioration of social life, which highlights the need to address the subjective factors (such as loneliness) and objective factors (such as social network size) of social isolation in a complementary way in order to improve the mental health of the older adult population.