A longitudinal study evaluated the success of a contact-based nation-building intervention (the Malaysian National Service Programme) in promoting various facets of national unity. The study assessed how post-test measures of quality of intergroup contact, outgroup evaluations, and levels of identification changed compared to their respective pre-test levels, for both National Service and control group participants. The intervention did not lead to a worsening of any of the constructs related to intergroup relations, which is noteworthy given the novelty for many participants of mixing in a multi-ethnic setting. Furthermore, all rater groups (Malays, Chinese, and Indians) maintained their ethnic identity, even in the presence of high levels of national identity, which we discuss with respect to past research on the effects of positive intergroup contact on minority group identification. However, the changes associated with the intervention yielded only small effect sizes, and, on the whole, National Service participants did not show significantly greater improvement than that experienced by control participants. We discuss the value of intergroup contact in this novel setting, considering various features of this programme that may have limited its effectiveness and discuss how such interventions can more successfully meet their goals.