Epidemiological studies investigating the mental health impacts of microaggressions in the trans population have tended to have methodological limitations, including a lack of validated measures, raising concerns about the validity of their findings. To address this evidence gap, we investigated the associations between microaggressions and poor mental health (depression; anxiety; non-suicidal self-harm [NSSH]; suicidal thoughts; suicide attempt) amongst trans people. We conducted a cross-sectional survey of 787 trans adults in the UK, measuring mental health and exposure to microaggressions using the Gender Identity Microaggressions Scale (GIMS). Using univariable and multivariable linear and logistic regression models we tested for an association of microaggressions with depressive symptoms (PHQ-9), anxiety symptoms (GAD-7), lifetime NSSH, lifetime suicidal thoughts, and lifetime suicide attempt. Of the 787 participants, 574 (73%) provided complete data. Microaggressions were a common experience, affecting 97.6% of participants over their lifetime. In adjusted analyses, using sociodemographic and clinical variables, increased microaggression scores were associated with increased depressive symptoms (adjusted coefficient: 1.86 (95%CI = 1.35 to 2.36)), anxiety symptoms (adjusted coefficient: 1.57 (95%CI = 1.09 -2.05)) and with increased odds of NSSH (Odds Ratio [OR]adj 1.83 (95%CI = 1.45 -2.30)), suicidal thoughts (ORadj 2.18, (95%CI = 1.52 -3.13)), and suicide attempt (ORadj, 1.59, (95%CI = 1.32 -1.92)). In exploratory analyses different GIMS subscales were associated with these various outcomes. There was evidence of associations between microaggressions and adverse mental health outcomes, as well as to support specific microaggressions being associated with specific outcomes, emphasizing the importance of public health interventions that target microaggressions directed at trans adults. Longitudinal studies are needed to investigate the temporality of the associations between microaggressions and mental health outcomes.