Here, we report the prevalence of loneliness and social isolation and investigate the levels of loneliness and social isolation among transgender and gender diverse people using cross-sectional data from the HH-TPCHIGV study. Using the De Jong Gierveld tool, we assess loneliness, using the Bude and Lantermann tool, we assess perceived social isolation and using the Lubben Social Network Scale, we assess objective social isolation. The prevalence rate of loneliness was 83.3% (perceived social isolation: 77.7%; objective social isolation: 34.4%). Regressions revealed that favorable outcomes (i.e., lower loneliness levels, lower perceived social isolation, and lower objective social isolation) were consistently associated with higher school education. Beyond that, we identify an association between particularly poor health-related factors and higher loneliness and objective social isolation levels. We also report that unemployment was significantly associated with higher levels of perceived social isolation. In conclusion, we show high prevalence rates of loneliness and social isolation among transgender and gender diverse people. Additionally, important correlates (e.g., education, health-related factors, or unemployment) were identified. Such knowledge may provide help to address transgender and gender diverse people at risk for loneliness and social isolation.