This thesis examines the abilities of constitutional mini-publics to make legitimate constitutions. Legitimacy in this thesis is defined as following the ideal of public reason. It is a quantitative study of the third weekend of the Irish Convention on the Constitution (a constitutional mini-public). They deliberated on and recommended amending the Constitution to allow same-sex marriage. Previous research into the legitimacy of constitutional mini-publics has been limited to studying their form, for example, participant selection or decision-making process. This thesis analyses the content of the deliberation. A series of theme analyses were performed to discover the reasons used. The reasons were categorised as public or nonpublic. The Convention on the Constitution justified all their decisions with public reasons. Showing constitutional mini-publics can make legitimate constitutions based on the ideal of public reason under the right circumstances.