Determinants of universal healthcare (UHC) are poorly empirically understood. We undertook a comprehensive study of UHC development using a novel Evidenced Formal Coverage (EFC) index that combines three key UHC elements: legal framework, population coverage, and accessibility. Applying the EFC index measures (legislation, ≥90% skilled birth attendance, ≥85% formal coverage) to 194 countries, aggregating time-varying data from 1880-2008, this study investigates which macro-economic, political, and social indicators are major longitudinal predictors of developing EFC globally, and in middle-income countries. Overall, 75 of 194 countries implemented legal-text UHC legislation, of which 51 achieved EFC. In a country-year prospective longitudinal analysis of EFC prediction, higher GDP-per-capita (per GDP-per-capita doubling, relative risk [RR]=1.77, 95% CI: 1.49-2.10), higher primary school completion (per +20% completion, RR=2.30, 1.65-3.21), and higher adult literacy were significantly associated with achieving EFC. Results also identify a GDP-per-capita of I$5000 as a minimum level for development of EFC. GDP-per-capita and education were each robust predictors in middle-income countries, and education remained significant even controlling for time-varying GDP growth. For income-inequality, the GINI coefficient was suggestive in its role in predicting EFC (p=0.024). For social and political indicators, a greater degree of ethnic fractionalization (per +25%, RR=0.51, 0.38-0.70), proportional electoral system (RR=2.80, 1.22-6.40), and dictatorships (RR=0.10, 0.05-0.27) were further associated with EFC. The novel EFC index and this longitudinal prospective study together indicate that investment in both economic growth and education should be seen of equal importance for development of UHC. Our findings help in understanding the social and political drivers of universal healthcare, especially for transitioning countries.