High-quality information to measure the need for, and the uptake, cost, quality and impact of care is essential in the pursuit of scaling up mental health care in low- and middle-income countries (LMIC). The aim of this study was to identify indicators for the measurement of effective coverage of mental health treatment. We conducted a two-round Delphi study (n = 93 experts from primarily LMIC countries Ethiopia, India, Nepal, Nigeria, South Africa and Uganda), in order to generate and prioritize a set of indicators. First, 52 unique indicators were generated (based on a total of 876 responses from participants). Second, the selected indicators were then scored for significance, relevance and feasibility. Mean priority scores were calculated per indicator (score range, 1–5). All 52 indicators had a weighted mean score that ranged from 3.20 for the lowest ranked to 4.27 for the highest ranked. The 15 highest ranked indicators cover the different domains of measuring effective mental health treatment coverage. This set of indicators is highly stable between the different groups of experts, as well as between the different participating countries. This study provides data on how mental health service and financial coverage can be assessed in LMIC. This is an important element in the move to scale-up mental health care.