Introduction: Recent research has revealed high rates of mental health issues in postgraduate researchers (PGRs). Mental ill-health is a barrier to life satisfaction and academic success. More knowledge is necessary to understand the extent and origins of mental health problems of PGRs in the UK. Aims: To assess the prevalence of anxiety, depression, sleep problems, subjective mental wellbeing, and suicide behaviours of PGRs in the UK, as well as to explore the factors that underpin these outcomes.Methods: An online survey (N=479) was used to measure the mental health outcomes, and assess the influence of demographic, trait and academic variables, and social support. Results: In this sample the prevalence of mental ill-health was high, while wellbeing was lower than in the general population. Female, non-binary and non-heterosexual PGRs had poorer mental health than their male and/or heterosexual counterparts. Researchers in the field of Arts had higher levels of wellbeing, while those in the 5th year of study or above were at a higher risk of suicidal behaviours. Resilience, adaptive perfectionism, social support and positive evaluations of progress and preparation, departmental climate, and supervisory relationship were associated with positive outcomes, while maladaptive perfectionism and workaholism were linked to the negative ones. Resilience and workaholism were the only variables that played a role in all mental health outcomes.Conclusions: The current paper contributes new knowledge about the PGR wellbeing, the prevalence of mental health symptoms, and some of the factors that shape them. Our findings imply that institutional efforts to improve PGR mental health and wellbeing should include a variety of strategies to promote equality, diversity, resilience, integration and work-life balance of PGRs.