Lesbian, gay and bisexual (LGB) consumers utilize mental health services at a similar rate to their heterosexual counterparts yet report greater dissatisfaction with service quality. This dissatisfaction may be explained by service provider's microaggressions, stemming from a lack of cultural competence in working with LGB consumers. This systematic review examines how the practises of mental health service providers impacted effective service provision to LGB people in a clinical practice. Five health databases (Scopus, MEDLINE, PsycINFO, Web of Science and CINAHL) were examined to determine relevant studies for this review. Twenty four qualitative and quantitative studies between 2000 and 2020 examining data related to how service provider practises impacted effective service provision to LGB people were included in the final review. A narrative synthesis, thematic summary approach was employed to account for the multi-method nature of the data. Themes developed in our analysis are organized under the three components of cultural competence, service provider attitudes, knowledge and skills. Provider attitudes ranged from positive to negative towards LGB people and heterosexism were present in several services. Poor service provider knowledge about the issues impacting LGB consumers leads to a weakened therapeutic alliance and service providers often lacked a comprehensive understanding of the issues impacting LGB people. Service providers were seen as more skilful if they were LGB, created a safe space and had completed cultural competence training. Trends within the characteristics (explorative nature, mixed service provider samples, potential for bias) of the 24 studies included in the review are discussed. Based on the results, recommendations are included to ensure services demonstrate cultural competence in working with LGB consumers.