Ontological security is the personal need to build fundamental certainty about the continuity of life events. It is central to long-term human development, particularly among adolescents in highly vulnerable communities in South Africa. We examined the cumulative effects of eight hypothesised provisions (development accelerators) in reducing the risks of ontological insecurity outcomes aligned with Sustainable Development Goals (SDGs) targets. Three waves of survey data from adolescents living in high HIV prevalence areas in South Africa were analysed. We used standardised tools to measure twelve outcomes linked to two dimensions of ontological security: mental health and violence. Sustained receipt (at baseline and follow-ups) of eight hypothesised accelerators were examined: emotional and social support, parental/caregiver monitoring, food sufficiency, accessible health care, government cash transfers to households, basic economic security, positive parenting/caregiving, and participation in extramural activities. Associations of all accelerators with outcomes were evaluated using multivariable regressions controlling for age, sex, orphanhood and HIV status, rural/urban location, and informal housing. Cumulative effects were tested using marginal effects modelling. Of 1,519 adolescents interviewed at baseline, 1,353 (89%) completed the interviews at two follow-ups. Mean age was 13.8 at baseline; 56.6% were female. Four provisions were associated with reductions in twelve outcomes. Combinations of accelerators resulted in a percentage reduction risk in individual indicators up to 18.3%. Emotional and social support, parental/caregiver monitoring, food sufficiency and accessible health care by themselves and in combination showed cumulative reductions across twelve outcomes. These results deepen an essential understanding of the long-term effects of consistent exposure to accelerators on multi-dimensional human development. They could be directly implemented by existing evidence-based interventions such as peer-based psychosocial support, parenting programmes, adolescent-responsive healthcare and food support, providing safer and healthier environments for South African adolescents to thrive.