We investigate how particular configurations of national parliaments affect the dynamics of political decentralization in parliamentary democracies. Recent research has emphasized the impact of structural determinants on levels of decentralization across countries. However, we argue that decentralization processes are endogenous to legislative bargaining by political parties. Our main hypothesis is that, ceteris paribus, the greater the legislative bargaining power of parties with decentralization demands, the more likely decentralization reforms are to occur. For that purpose, we calculate an index of the parliamentary salience of decentralization that reflects the distribution of parties’ preferences for decentralization weighted by their bargaining power. We test our hypotheses with dynamic models for 19 parliamentary democracies using Comparative Manifesto Project data and the Regional Authority Index. We demonstrate that the dynamics of decentralization are crucially shaped by the configuration of national legislatures, although this only seems to affect the self-rule dimension of decentralization rather than shared rule.