Stakeholder engagement in the design and formulation of legislative proposals and public policies is a landmark of modern policymaking in advanced democracies. Stakeholder consultations are particularly relevant for non-elected institutions, such as executive bureaucracies, for which stakeholder engagement represents a unique opportunity to build input and throughput legitimacy and to gather (broad) public support for their proposed policies. When and how the constellation of different consultation mechanisms affects the levels of stakeholder support for legislative proposals constitutes a key theoretical and empirical puzzle that currently remains unaddressed in a systematic manner in the literature on stakeholder engagement in democratic policymaking. The study addresses this gap and focuses empirically on one of the most complex and institutionalized stakeholder consultation regimes: that implemented by the European Commission since 2016 when the European executive significantly expanded the scope and breath of stakeholder engagement across different stages of its policy formulation processes. The study examines the extent to which different consultation mechanisms (i.e., online consultations, feedback opportunities, etc.) employed when formulating European policies shape the levels of stakeholder support for draft legislative proposals across different policy areas. The study elaborates an argument explaining how institutional characteristics of consultation design, characteristics of stakeholder participation in consultations and key characteristics of policy areas contribute towards explaining the conditions under which public consultation mechanisms elicit varying levels of stakeholder support. This argument is tested on a new dataset recording information about stakeholder consultations and expressed stakeholder support for 469 EC draft legislative proposals adopted during the 2016-2021.