How do we know whether psychological science generalises across groups? External validity, including the nomological network, is key for establishing the utility of psychological constructs in under-investigated populations. We used an online, monthly longitudinal study measuring personality, social relationships and mental health. Among participants (total N = 1777; 31% retention), 73% identified as sexual and/or gender minority (SGM). Longitudinal growth parameters, rank-order stability and cross-time correlations were examined. The findings showed remarkably similar associations and rank-order stability. Mean differences measured using multiple assessments displayed a similar pattern to cross-sectional differences with slightly diminished magnitudes. These exploratory results can inform longitudinal research to be better equipped to disentangle processes that support resilience in the face of extant negative influences, address health disparities and identify associations that are more universal in the studied contexts lending support for diversifying psychological research across SGM identities.