St. Patrick’s Day as a March 17 holiday was fixed on the liturgical calendar in the early 1600s according to New Advent, though feasts commemorating Patrick were observed in Ireland as early as the 9th century. As a holiday within Lent, it was seized upon as an excuse to be free of Lenten prohibitions, and the Catholic Church turned to the green shamrock to reinforce the day’s intended meaning. At the time, the color most associated with Saint Patrick and Ireland was still blue, but there was a custom of plucking shamrocks to place in one’s lapel on the holiday.
A Catholic uprising in 1641 saw an army out of Kilkenny use a green flag with a gold harp. But it was the Rebellion of 1798, begun that February, that most helped tie green to the idea of Irish rebellion from Britain. The fight of 1798 was a brief one; per the Museum of the American Revolution, it only lasted five months. But it was an early push by the Irish for a republican government, inspired by the recent examples of America and France.
The French Revolution provided inspiration of a different kind. Just as revolutionaries in France donned distinctive caps, the Society of United Irishmen had their own unique clothing at a time when military uniforms took on symbolic importance. A police report (via Alexander Maxwell’s “Patriots Against Fashion”) described the Irish rebel uniform as a dark green coat with green and white-striped trousers and a shamrock as the rebels’ device.
