On the basis of internal sources (biographies, individual assessments) and of a socio-biographic analysis of the intermediate cadre of members of the French Communist Party (PCF), this paper focuses on the access of activists with a working class background to the status of permanent party cadre from 1945 to 1968. From the party’s point of view, the search for the 'tomorrow’s cadres’ tends to benefit a certain type of factory-based activists who are not characterized by the routine practices of union bureaucracies but mobilize resources and knowledge outside the factory. Yet, this 'promotion’ is paradoxical. It requires a social and cultural displacement that sometimes fuels avoidance, distancing, or refusal, in particular through the concentration on shop floor or union activism as a form of preservation of working class identity. On the contrary, for the cadres better adapted to this role, assimilation to the working class stems from their calling for political activism. Despite being in a position to enjoy other social roles, they adopt the social identity most valued by the Party, mirroring other patterns of engagement centered on the working class