In this paper we analyse—theoretically and empirically—how the degree of private versus public ownership of firms affects the degree of rent sharing between firms and their workers. Using a particularly rich linked employer-employee dataset from Portugal, covering a large number of corporate ownership changes across a wide spectrum of economic sectors over more than 20 years, we find that rent sharing is significantly higher in firms with a larger share of private ownership. Estimates from our most preferred empirical specification suggest that an increase in the private ownership share of 10 percentage points increases (on average) the rent-sharing elasticity by 0.0002. Based on a theoretical analysis that incorporates union-firm wage bargaining and efficiency wage effects within the same modelling framework, this result cannot be explained by private firms being more profit oriented than public ones. However, the result is consistent with a scenario whereby privatisation leads to less job security for workers, implying stronger efficiency wage effects.