Objective We sought to classify causes of stillbirth for six low‐middle‐income countries using a prospectively defined algorithm. Design Prospective, observational study. Setting Communities in India, Pakistan, Guatemala, Democratic Republic of Congo, Zambia and Kenya. Population Pregnant women residing in defined study regions. Methods Basic data regarding conditions present during pregnancy and delivery were collected. Using these data, a computer‐based hierarchal algorithm assigned cause of stillbirth. Causes included birth trauma, congenital anomaly, infection, asphyxia, and preterm birth, based on existing cause of death classifications and included contributing maternal conditions. Main outcome measures Primary cause of stillbirth. Results Of 109 911 women who were enrolled and delivered (99% of those screened in pregnancy), 2847 had a stillbirth (a rate of 27.2 per 1000 births). Asphyxia was the cause of 46.6% of the stillbirths, followed by infection (20.8%), congenital anomalies (8.4%) and prematurity (6.6%). Among those caused by asphyxia, 38% had prolonged or obstructed labour, 19% antepartum haemorrhage and 18% pre‐eclampsia/eclampsia. About two‐thirds (67.4%) of the stillbirths did not have signs of maceration. Conclusions Our algorithm determined cause of stillbirth from basic data obtained from lay‐health providers. The major cause of stillbirth was fetal asphyxia associated with prolonged or obstructed labour, pre‐eclampsia and antepartum haemorrhage. In the African sites, infection also was an important contributor to stillbirth. Using this algorithm, we documented cause of stillbirth and its trends to inform public health programs, using consistency, transparency, and comparability across time or regions with minimal burden on the healthcare system. Tweetable Major causes of stillbirth are asphyxia, pre‐eclampsia and haemorrhage. Infections are important in Africa. Tweetable Major causes of stillbirth are asphyxia, pre‐eclampsia and haemorrhage. Infections are important in Africa.