Abstract: The impact of reduced social contact on mental health during the COVID-19 pandemic has been identified as a major public health concern. While personality factors such as attachment style have been associated with psychological distress during the pandemic, the longitudinal relevance of these factors and the role of daily social contact in mitigating distress remains poorly understood. This study evaluated the impact of social contact and attachment style on changes in loneliness over an 8-week experience sampling period during the COVID-19 pandemic. A general adult sample (n = 184) recruited online completed measures of psychological distress, attachment, and loneliness via smartphone. Loneliness and daily social contact were assessed twice per week for eight weeks, yielding 1124 unique observations. During the experience sampling period, proximal increases in loneliness were associated with decreased daily in-person contact. In contrast, participants who described themselves as having fewer interactions via text, phone, or videoconferencing, as well as those with higher anxious and avoidant attachment traits, reported greater experiences of loneliness over time. These findings suggest the relevance of both enduring personality characteristics and daily social behaviors as risk factors for loneliness during the pandemic, pointing to potential targets for clinical intervention and future empirical study.