In June 2014, the Human Rights Council passed a resolution establishing an inter-governmental working group to discuss a legally binding instrument relating to transnational corporations and other business enterprises. In this article, I outline four arguments for why such an instrument is desirable. Identifying the purpose of such a treaty is crucial in outlining a vision of what it should seek to achieve and in determining its content. The arguments indicate that a treaty is necessary to provide legal solutions to cure serious lacunae and ambiguities in the current framework of international law which have a serious negative impact upon the rights of individuals affected by corporate activities. The emphasis throughout is upon why a binding legal instrument is important, as opposed to softer forms of regulation such as the United Nations Guiding Principles on Business and Human Rights. The four arguments in turn provide the resources to respond to objections raised against the treaty and to reject an alternative, more restrictive proposal for a treaty that only addresses ‘gross’ human rights violations.