The appeal of constitutional referendum as legitimating tools revolves around their participatory promise. Recent work has also argued in favour of referendums’ potential as deadlock breaking and even peacemaking tools in divided and post-conflict societies. This paper investigates a not uncommon scenario that plays out in such instances: referendum boycotts. One or several of the key players in the polity may call for a referendum boycott in order to block or delegitimise the peacemaking or constitutional change reform process. The international community itself may see a boycotted referendum as evidence of the process’s lack of democratic credentials. This paper draws on comparative practice to investigate the questions raised by boycotted referendums and options to avoid or manage boycotts, as well as how boycotted referendum results are to be interpreted. The backdrop to this investigation is a possible ‘border poll’ on Irish unification and the risk of a boycott therein.