Collaborative governance institutions consisting of government and civil society actors often emerge to solve complex policy problems. Yet decades of research on collaborative governance has found that realizing the ‘collaborative advantage’ is often very difficult given the multitude of actors, organizations and interests to be managed. This article deploys a participant observation approach that also harnesses data from a natural experiment in collaborative governance for homelessness policy in Vancouver, Canada, to reveal the distinct collaborative advantage produced in terms of policy, using empirical decision data and counterfactual analysis. The data reveal that nearly 50 per cent of the policy decisions made in the collaborative institution would not be made in the alternative scenario of unilateral bureaucratic control. The collaborative advantage realized in this governance institution that is premised on horizontality, deliberation and diversity is the result of a series of small interventions and the strategic deployment of rules devised by the bureaucratic metagovernor in charge of steering the governance collaboration.