Despite the importance for both animal welfare and scientific integrity of effective welfare assessment in non-human primates, there has been little or no consensus as what should be assessed. A Delphi consultation process was undertaken to identify the animal- and environment-based measures of welfare for laboratory-housed macaques and to determine their relative importance in on-site welfare assessments. One-hundred fifteen potential indictors were identified through a comprehensive literature search, followed by a two-round iterative electronic survey process to collect expert opinion. Stable group response and consensus about the validity, reliability, and feasibility of the proposed indicators (67.5% agreement) was achieved by the completion of Round Two. A substantially higher proportion of environment-based measures (72%: n = 44/61) were considered as valid, reliable, and feasible compared to the animal-based measures (22%: n = 12/54). The indicators that ranked most highly for assessing welfare were the presence of self-harm behaviours and the provision of social enrichment. This study provides an empirical basis upon which these indicators can be validated and then integrated into assessment tools developed for macaques and emphasises the need to include both animal- and environment-based indicators for accurate welfare monitoring.