Abstract Social connectedness has been conceptualised in diverse ways across the psychological and social sciences, with relationship quality, family support, trust, neighbourhood cohesion, and loneliness often examined separately. The present study examined whether these experiences represent distinct social phenomena or manifestations of a broader underlying social connectedness construct. Data were drawn from 41,242 participants from the United Kingdom Household Longitudinal Study. Confirmatory factor analyses compared competing representations of social connectedness, followed by structural equation modelling to examine associations with psychological wellbeing outcomes. Results indicated that a three-factor model comprising relational connectedness, community connectedness, and subjective disconnectedness provided the best balance of fit and theoretical parsimony. These dimensions were strongly interrelated and were adequately represented by a higher-order social connectedness factor, consistent with a hierarchical conceptualisation of the construct. The higher-order factor was strongly associated with lower psychological distress and higher life satisfaction, mental wellbeing, and mental health-related quality of life, accounting for 56% to 63% of the variance in psychological wellbeing outcomes. Associations with physical health-related quality of life were comparatively modest. Correlated-factors analyses indicated that community connectedness was most strongly associated with life satisfaction and mental health-related quality of life, whereas subjective disconnectedness was most strongly associated with psychological distress. These findings suggest that social connectedness may be usefully understood as a multidimensional but integrated psychological construct, linking relational, community, and subjective dimensions within a unified framework. Clinical Trial Number Clinical trial number: not applicable