Socioeconomic inequalities in mortality are large and persistent. While the differential timing and impact of the smoking, alcohol, and obesity epidemics among socioeconomic groups likely influenced past trends in socioeconomic mortality inequalities, the evidence is scarce. We estimated the combined impact of smoking, alcohol, and obesity on past trends in educational inequalities in remaining life expectancy at age 30 (e30) in England and Wales, Finland, and Italy (Turin). To do so, we used long-term timeseries of annual individually-linked mortality data by educational level (low, middle, high), sex, and age (30+). We multiplicatively aggregated estimates of smoking-, alcohol-, and obesity-attributable mortality by educational level to obtain "lifestyle-attributable mortality" (LAM) by educational level. We compared trends in educational inequalities in e30 with and without LAM using segmented regression. We found that smoking-, alcohol-, and obesity-attributable mortality individually contributed 23%, 14%, and 10%, respectively, to the average educational inequality in e30 of 4.4 years in 1992-2017, and 44% combined (males: 51%; females: 34%). LAM contributed 57%, 63%, and 43%, respectively, to the increase in educational inequalities in e30 among Finnish males (1987-2008), Finnish females (1987-2017), and Italian males (1990-2018); tempered the decline in inequalities among British females (1992-2017); and was responsible for the reversal in 2008 from increasing to declining inequalities among Finnish males. Targeting socioeconomic inequalities in smoking, alcohol, and obesity could, thus, substantially reduce socioeconomic inequalities in e30, and the increasing time trends in these inequalities. The observed country differences in the importance of these lifestyle factors demonstrate the need for context-specific strategies.