BACKGROUND: HIV self-testing (HIVST) may facilitate marginalised populations' uptake of HIV testing, but whether the extent of marginalisation challenges individual uptake of HIVST remains under-researched. We aim to explore the perspectives of multiply marginalised cis-gender gay, bisexual and other men who have sex with men (GBMSM) and trans women on whether HIVST might increase their uptake of HIV testing. METHODS: We reanalysed qualitative interview data from SELPHI (the UK's largest HIVST randomised trial) collected between 2017 and 2020 from marginalised populations, defined as people self-identifying as non-heterosexual, transgender, non-White ethnicity and/or with low educational attainment. Thirty-eight interviews with multiply marginalised individuals were thematically examined using the framework method. We specifically focussed on kit usability (a function of the interaction between blood-based HIVST kits and users), perspectives on how HIVST can improve access to HIV testing and suggestions on need-based scale-up of HIVST. RESULTS: HIVST kits were considered usable and acceptable by multiply marginalised GBMSM and trans women. The majority of interviewees highlighted multi-levelled barriers to accessing HIV testing services due to structural and social marginalisation. Their multiply marginalised identities did not impede HIVST uptake but often form motivation to self-test. Three potential roles of HIVST in the HIV testing landscape were identified: (1) alternation of HIVST and facility-based testing, (2) integration of HIVST into sexual health services and (3) substituting facility-based testing with HIVST in the future. Perceived beneficiaries of HIVST included trans communities, individuals with undisclosed sexuality and people with physical disabilities. DISCUSSION: HIVST can facilitate marginalised populations' access and uptake of HIV testing by alternating with, integrating into and substituting for facility-based services in the UK. Marginalised identities did not present challenges but rather opportunities for person-centred scale-up of HIVST. Future implementation programmes should ensure equitable access to HIVST among trans people, men unable to disclose their sexuality, and perhaps people with physical disabilities.