This paper examines the working of the first Irish Constitutional Convention held in 2013. It was argued that using a deliberative approach to reform the Constitution would be valuable as it would directly involve citizens in decisions of constitutional reform, thereby enhancing diminished democratic legitimacy and potentially re-configuring democratic practice. The Convention led to a referendum to recognize marriage equality, with Ireland becoming the first country to institute such equality by popular vote. This paper examines all facets of the Convention, deploying a framework of input, throughput, and output legitimacy. We find that it is in two of the areas that were initially a strong source of criticism—its composition and remit—that the Convention has been truly innovative in ways that have contributed to its legitimacy across multiple dimensions.