Background: Young adults who are lesbian, gay, bisexual, trans, queer or questioning, intersex, asexual and other diverse genders and sexualities (LGBTQIA+) are more likely to experience mental health difficulties and are at significantly elevated risk of substance abuse, self-harm and suicide, relative to their heterosexual, endosex and cisgender peers. There is a need for effective mental health interventions for LGBTQIA+ young adults. Mindful Self-Compassion training is a promising approach; among LGBTQIA+ individuals, self-compassion accounts for more variation in mental health outcomes than bullying, victimization, and adverse childhood experiences combined. Furthermore, LGBTQIA+ individuals with high self-compassion report more positive identity and happiness, less self-stigma, and lower suicidality than those with low self-compassion. Method: This paper outlines the rationale and protocol for a single-blind CONSORT-compliant randomised controlled trial, comparing group Mindful Self-Compassion to a delayed-treatment waitlist control group, for improving mental health, decreasing self-criticism and increasing self-compassion in LGBTQIA+ young adults (age 18–25 years). Mindful Self-Compassion training is an 8-week group program that focuses on cultivating self-compassion and mindfulness. While typically delivered as a face-to-face program, the proposed trial will investigate efficacy of the program when provided via videoconferencing. Discussion: Videoconference Mindful Self-Compassion training has the potential to improve the mental health of Australian LGBTQIA+ young adults and provide a possible cost-effective, scalable intervention for this population. The proposed trial will be the first to determine its efficacy for LGBTQIA+ young adults and will provide the first data on the delivery of the program via videoconferencing.