Sweeping societal changes during the latter 20th and early 21st centuries have resulted in considerably different developmental trajectories among present-day 18- to 25-year-olds (i.e., emerging adults) with respect to those of prior generations. The experience of emerging adulthood is associated with considerable demographic instability, identity testing, and extended moratorium from seeking and attaining adult roles. A growing body of research has suggested that such experiences have resulted in difficulty and distress for many emerging adults as they progress through the various normative life transitions (e.g., entering the workforce) associated with this age group. The present study sought to add understanding to this problem by exploring the associations among attachment, social support, subjective well-being, and psychological well-being for emerging adults experiencing life transition. This study utilized a non-experimental survey design with a sample of participants between the ages of 18 and 27. A theoretical mediation model was developed, which predicted that perceived social support would mediate the relationships of attachment anxiety and attachment avoidance on subjective well-being and psychological well-being. Several other models were developed based on discursive literature to determine whether or not the mediation model provided the best fit to the sample data. The models were tested using structural equation modeling, and the significance of the mediation effects were tested using bias-corrected bootstrap analyses. The results indicated significant and negative relationships among each attachment variable on each well-being variable. Additionally, perceived social support significantly mediated each of these direct relationships. Analysis of the alternative models revealed that an alternative mediation model, in which psychological well-being mediated the relationships of attachment anxiety, attachment avoidance, and perceived social support on subjective well-being, was the best fit to the data. Through the alternative model testing, significant moderation effects were also discovered between perceived social support and attachment avoidance. After several model modification steps, the alternative mediation model provided an excellent fit to the data. The findings are discussed in the context of other emerging adult and attachment research. Implications for counseling theory and practice are considered, and suggestions for future research are provided.