How has the European Parliament’s relative power in EU legislative negotiations changed since the Lisbon Treaty? This article provides the first systematic comparison of legislative power before and after Lisbon by estimating the relative influence of the European Parliament, Council of the EU, and European Commission across 417 controversial policy issues negotiated between 1998 and 2024. It tests two contrasting expectations: one derived from liberal intergovernmentalism, which holds that the Treaty should have changed little about the balance of power; and an institutionalist perspective which allows for more substantial and potentially unexpected shifts following institutional change. The results provide clear support for the latter proposition. The Parliament’s inferred weight more than doubles after Lisbon, the Commission’s declines sharply, and the Council’s dominance diminishes. Notably, these changes occur even for policy areas already governed by co-decision before Lisbon, indicating that the Treaty’s effects cannot be attributed solely to official rule changes.