A growing body of research has highlighted the adverse impact of COVID-19 stressors on health and social care workers' (HSCWs) mental health. Complementing this work, we report on the psychosocial factors that have had both a positive and negative impact on the mental well-being of HSCWs during the third lockdown period in Scotland. Using a cross-sectional design, participants (n = 1364) completed an online survey providing quantitative data and free open-text responses. A multi-method approach to analysis was used. The majority of HSCWs were found to have low wellbeing scores, high levels of COVID-19 stress, worry, burnout and risk perception scores and almost half of HSCWs met the clinical cut-off for acute stress (indicative of PTSD). HSCWs with higher scores on adaptive coping strategies and team resilience reported higher scores on mental well-being. HSCWs were significantly more likely to seek informal support for dealing with personal or emotional problems compared to formal supports. Barriers to formal help-seeking were identified including stigma and fear of the consequences of disclosure. HSCWs mostly valued peer support, workplace supports, visible leadership and teamwork in maintaining their mental well-being. Our findings illuminate the complexity of the effects of the COVID-19 pandemic on HSCWs' well-being and will inform future intervention development seeking to increase positive adaptation and improve staff well-being. Addressing barriers to mental health help-seeking among HSCWs is essential. The implications emphasise the importance of lessons learned across health and social care contexts, planning and preparedness for future pandemics.