Over the last two decades, social capital has received increasing attention in the international literature. Despite the popularity of the construct, problems concerning definition, theoretical conceptualisation, and measurement continue to plague research and policy in this area. This investigation aimed to address this gap by developing a new social capital instrument to test the theorised nature of the construct. Utilising a sample of 1371 young Australians living in disadvantaged communities, the newly developed Social Capital and Cohesion Scale (SCCS) combined the commonalities in the current theoretical conceptualisations of social capital defining it as a multi-level, multidimensional construct consisting of trust and reciprocity across family, peer, neighbour, and institutional networks. To test the convergent validity of the scale, relations with mental health were also examined. Confirmatory factor analysis results demonstrated that the SCCS was a valid and reliable multidimensional scale, which was invariant across both regional and gender groups. Correlational analysis demonstrated that associations with depression, anxiety, and stress were consistent with past research thereby strengthening the validity of the SCCS measure.