Lesbian, gay, bisexual, transgender, and questioning youth of color (LGBTQ-YOC) face disproportionate risks of adverse mental health outcomes, including higher rates of depression and suicide-related thoughts and behaviors (STB) compared to their White LGBTQ and heterosexual peers. Despite the documented disparities, there is a critical lack of developmental research examining trajectories of depression and STB among LGBTQ-YOC. This dissertation addresses this gap by examining the longitudinal trajectories of depression and STB among Black/African American and Hispanic/Latinx LGBTQ-YOC. Data from 19 longitudinal studies (N = 29,428), including 18 prevention trials and one observational study, were harmonized and analyzed as a pooled dataset using integrated data analysis to address two primary aims: 1) investigate developmental patterns of depression and STB from early adolescence to young adulthood (10 to 18 years), and 2) to identify early depression symptoms associated with a higher risk of STB trajectories. Analyses were conducted with a subsample of Black/African American (n = 1,069) and Hispanic/Latinx LGBTQ-YOC (n = 1,321). Multilevel growth curve modeling and latent class growth mixture modeling were used to examine the longitudinal trajectories of depression and STB and to identify subgroups with distinct latent classes. Growth curve modeling revealed peak depression and STB symptoms between ages 14-16 across both groups. Latent class analyses identified distinct trajectory patterns, with most youth exhibiting stable low symptoms while smaller subgroups showed increasing or decreasing severity over time. Female-identified, transgender and bisexual youth showed consistently higher risk compared to male and gay/lesbian peers. Feelings of worthlessness and hopelessness emerged as significant predictors of high-risk trajectories for all forms of STB. Other significant associations were found for sleep and appetite problems, guilt, sad/depressed mood, anhedonia, loneliness, fear, and psychomotor changes. Mixed findings were found for anxiety, worry, and concentration problems on STB risk trajectories. These findings advance our understanding of how depression and STB manifest differently across development for Black/African American and Hispanic/Latinx LGBTQ-YOC. By identifying critical risk periods, vulnerable subgroups, and early warning signs specific to each population, this research provides an empirical foundation for culturally responsive prevention and intervention approaches. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]