In 1792 Birch joined the United Irishmen, intervening with them in a crucial Bastille Day Volunteer debate in Belfast to defend a resolution in favour of immediate, unqualified, Catholic emancipation. He regarded the "withholding of rights from our Catholic brethren" and "criminally unjust and impolitic", and declared "He would rather, he transport himself to Botany Bay, than live in a country which continued to keep itself in abject slavery, by its internal divisions".