BACKGROUND: Sub-Saharan Africa and southern Asia account for almost 85% of global maternal deaths from post-partum haemorrhage. Early administration of tranexamic acid, within 3 h of giving birth, was shown to reduce the risk of death due to bleeding in women with post-partum haemorrhage in the World Maternal Antifibrinolytic (WOMAN) trial. We aimed to assess the cost-effectiveness of early administration of tranexamic acid for treatment of post-partum haemorrhage. METHODS: For this economic evaluation we developed a decision model to assess the cost-effectiveness of the addition of tranexamic acid to usual care for treatment of women with post-partum haemorrhage in Nigeria and Pakistan. We used data from the WOMAN trial to inform model parameters, supplemented by estimates from the literature. We estimated costs (calculated in 2016 US$), life-years, and quality-adjusted life-years (QALYs) with and without tranexamic acid, calculated incremental cost-effectiveness ratios (ICERs), and compared these to threshold values in each country. Costs were assessed from the health-care provider perspective and discounted at 3% per year in the base case analysis. We did a series of one-way sensitivity analyses and probabilistic sensitivity analysis to assess the robustness of the results to parameter uncertainty. FINDINGS: Early treatment of post-partum haemorrhage with tranexamic acid generated an average gain of 0·18 QALYs at an additional cost of $37·12 per patient in Nigeria and an average gain of 0·08 QALYs at an additional cost of $6·55 per patient in Pakistan. The base case ICER results were $208 per QALY in Nigeria and $83 per QALY in Pakistan. These ICERs were below the lower bound of the cost-effectiveness threshold range in both countries. The ICERs were most sensitive to uncertainty in parameter inputs for the relative risk of death due to bleeding with tranexamic acid, the discount rate, the cost of the drug, and the baseline probability of death due to bleeding. INTERPRETATION: Early treatment of post-partum haemorrhage with tranexamic acid is highly cost-effective in Nigeria and Pakistan, and is likely to be cost-effective in countries in sub-Saharan Africa and southern Asia with a similar baseline risk of death due to bleeding. FUNDING: London School of Hygiene & Tropical Medicine, Pfizer, UK Department of Health, Wellcome Trust, and Bill & Melinda Gates Foundation.