O Verile de conventionality is an important mechanism used to promote the alignment of the Brazilian sub-constitutional legal system with international human rights treaties. Still poorly used by lawyers, verification of voluntary agreements in its diffuse form is the subject of a study in the context of the Brazilian civil procedure. The purpose of this work is to analyse the conduct of that control in the light of the principles of due legal process, adversarial procedure and extensive defence, as well as with regard to the rules and other principles set out in the 2015 Code of Civil Procedure, including, in particular, the one providing for the fence of ‘surprise decisions’ in the procedural context, listed in Article 10 of that law. The method used will be the deductive method and the methodological technique will be theoretical research, based on an analysis of bibliographic research, legislation and case-law, for the application of the proposals and conclusions in the specific case. It will be possible to verify, as a result, how the control of diffuse agreement should be carried out, while respecting the procedural rules of the Democratic State of Law.