This paper discusses aggregate meetings of Dublin in the early nineteenth century. An aggregate meeting was an ad hoc meeting held to mobilise and express public opinion on various issues. While the chief promoters of aggregate meetings in eighteenth-century Dublin were Protestants who demanded political reforms, after the formation of the United Kingdom in 1801 Catholics began to convene their own aggregate meetings to prepare petitions to the Westminster Parliament for Catholic emancipation. Because other forms of Catholic political activities were banned by the government, Catholic politicians relied increasingly on aggregate meetings, which became an annual event in Dublin. Catholic aggregate meetings sometimes collected a few hundred people and enjoyed wide newspaper coverage, against which conservative (anti-Catholic emancipation) Protestants could mobilise only a small number of people at its regular meetings, which made them inferior to Catholics in terms of publicity. Aggregate meetings in Dublin widened their scope as the city saw a surge of monarchical loyalism in 1820-21, when not only liberal (pro-Catholic emancipation) Protestants and Catholics but also conservative Protestants joined combined aggregate meetings to celebrate the coronation of the new king. Although a new phenomenon, it was temporary, as conservative Protestants soon seceded from the alliance. However, the narrowing of the scope did not lead to the diminishing of the significance of aggregate meetings. In fact, the most influential aggregate meeting was a combined meeting of liberal Protestants and Catholics that created and spread an unrealistic definition of the nature of a criminal case, resulting in deforming the legal process of the case.