In the past years we have seen a somewhat paradoxical evolution in EU trade politics. While the Lisbon Treaty was meant to facilitate the adoption of trade agreements by bolstering the exclusive supranational competence of the European Union, (sub-)national Parliaments have now become more involved in trade policy than ever before. We investigate this shift in involvement across the Belgian parliaments. In the past fifteen years, both the Federal, Flemish and Walloon parliament paid little attention to EU trade policy. This has changed since 2014, especially in Wallonia but also in the other assemblies. Combining a variety of sources, we conclude that several interacting factors have fuelled this increase in Parliamentary involvement. First, TTIP and CETA contain ‘deep trade’ provisions that have alerted MPs. Second, TTIP has generated an unseen amount of mobilisation and contestation, and this has led politicians (especially on the left and in the opposition) to join the fray as well. Finally, the asymmetry between the Walloon and federal governing coalitions have favoured a more activist opposition by Wallonia, while Flanders’ centre-right coalition has remained supportive.