The COVID-19 pandemic and associated restrictions significantly disrupted the delivery of mental health services, worsened the mental health of the population, and exacerbated existing health inequalities. Whilst COVID-19 disproportionately increased the presentation of mental health difficulties for lesbian, gay, bisexual, transgender, and queer (LGBTQ+) people, limited evidence exists on how it may have impacted inequalities in access to mental health services for these population groups. Therefore, this thesis presents mixed methods research which aimed to explore access to mental health services for LGBTQ+ people during the COVID-19 pandemic. First, a systematic mapping review was undertaken to understand how inequalities in access to adult mental health services in the UK have been researched previously. Second, routinely collected NHS mental health service data were analysed to explore the feasibility of examining variations in access by sexual orientation and how these changed during COVID-19. Finally, topic-guided interviews were conducted with LGBTQ+ people who accessed mental health services during the pandemic to explore their experiences of access. Levesque’s Conceptual Framework for Healthcare Access was adopted throughout this research to conceptualise what was meant by “access”. The review emphasised a need for mixed methods research to examine access to mental health services for LGBTQ+ people. Together, the primary research studies generated insight into the disproportionate effects that the COVID-19 pandemic had on LGBTQ+ people, through an increased risk of mental ill health from isolation and loss of social connectedness, and unique challenges in negotiating access to mental health services under crisis conditions, such as insufficient resources, experiences of stigma, and concealing their identity. This thesis concludes that much remains to be done within policy to prioritise the potential vulnerabilities of LGBTQ+ people and mitigate against disproportionate effects in the event of future crises. Improvements in sexual orientation and gender identity data collection and the inclusivity of mental health services, by enhancing the knowledge and competencies of professionals providing mental healthcare to LGBTQ+ people, is recommended to address the poor experiences of LGBTQ+ service users.