This article draws on empirical evidence from a trade union in the centre of Athens to explore the impact of a politically active membership and its dialectical relationship with union renewal. The examined union is considered as an exemplar for the Greek accounts of unionism in the sense that it has achieved considerable collective bargaining gains and it has organized successful membership mobilization stories. It is argued in the analysis that the success of this union stems from a strategy of making rank-and-file activists the very fabric of union’s organizing and mobilization activities. Further, trust issues between leaders, activists and ordinary members are significant in the increase of the likelihood of collective action.