From an ethical standpoint, transparency is an essential requirement in public policy-making. Ideally, policy-makers are transparent and actively disclose the presence, purpose and means of a decision aid. From a practical point of view, however, transparency has been discussed as reducing the effectiveness of decision aids. In the present paper, we elaborate on how transparency affects the effectiveness of defaults. In three experiments, we manipulated whether the endorser was transparent about the default or not and assessed participants’ decisions to opt out or comply. Throughout the experiments, we found that proactive transparency reduced opt-out rates as compared to a non-transparent default condition. Moreover, proactive disclosure of a default reduced opt-out rates as compared to informed control groups, where participants imagined they had retrieved the default-related information by themselves (Studies 1 and 2). The results further indicate that a lack of proactive disclosure may lead targets to perceive the endorser as less sincere and to feel deceived, which in turn hinders the effectiveness of the default. In general, our findings lend support to the proactive transparency paradigm in governance and show that a default-based policy can be transparent and effective at the same time.