Mortality differentials between French occupations and occupational classes are large and widening. But considerable inequalities also exist within occupational classes by career history. Changes in the labour market and occupational pathways in recent decades – notably among women – have altered the composition of occupational classes and their average mortality levels. This article analyses the changes in mortality differentials between occupational classes by studying occupational mobility and associated mortality using data from the permanent demographic sample (Échantillon démographique permanent, EDP), a long-term sample representative of the French population at different dates. Analysis of mortality in 1975 (EDP75) and 1999 (EDP99) by occupational class and past occupational moves shows that mortality has declined for all classes but in different ways, causing a slight widening of differentials for both sexes. Within occupational classes, differentials by past moves increased in the EDP99 for men and were now observed in all classes for women. Changes in the composition of occupational classes and in excess mortality associated with certain moves has contributed to this increase in inequalities between occupational classes. This finding highlights the importance of interpreting changes in mortality differentials in the light of sociodemographic developments.