7 March 1848: The Irish Tricolour/ Trídhathach na hÉireann was first flown in public on this day. The event took place in Waterford when Thomas Francis Meagher raised it over at the Wolf Tone Confederate Club at 33 The Mall in that city.

The Tricolour idea came from France where it was symbolised by the colours Red White and Blue to emphasise concord between the social classes and had been given a new wave of enthusiasm by the February Revolution that had just overthrown King Louise Phillippe.

‘Prior to this, the wearing of green, white and orange rosettes and cockades had started to become common in Ireland, as an expression of the dream of a united Irish people. The French tricolour also appeared in support of the concurrent revolution in France, an event that had greatly inspired the young Meagher. After Meagher’s innovation the Irish tricolour started to appear at rallies and bonfires across the nation.’

But his flying the Tricolour was not to everyone’s taste: ‘In March 1848 a concerned mayor of Waterford, Sylvester Phelan, wrote to T.N. Reddington, under-secretary for Ireland, asking what action he should take in relation to an Irish tricolour hanging from 33 The Mall. The reply the mayor received is unclear, but records show that the flag was still flying ten days later. Thomas Francis Meagher had unveiled a tricolour that would eventually become the national flag of Ireland at the Wolfe Tone Club in Waterford.’

‘In April 1848 Meagher and William Smith O’Brien travelled to France to seek support for their cause. Alphonse de Lamartine, head of the provisional government, was reluctant to provide direct support to the young idealists. The Young Irelanders returned from France with a fabulous silken tricolour, however, which they presented to the other members of the Irish Confederation on 15 April 1848.’

https://www.historyireland.com/uncategorized/1848-tricolour-celebration/

Meagher stated that:

“…I trust that the old country will not refuse this symbol of a new life from one of her youngest children. I need not explain its meaning. The quick and passionate intellect of the generation now springing into arms will catch it at a glance. The white in the centre signifies a lasting truce between the “orange” and the “green” and I trust that beneath its folds, the hands of the Irish Protestant and the Irish Catholic may be clasped in generous and heroic brotherhood…” 

However the flag never really caught on and the old flag of a golden harp on a Green background remained in favour in Nationalist circles right up the 1916 Rising. But in that year it was flown over the GPO in Dublin as the symbol of the new Republic and its popularity soared.

It was adopted as the flag of the Irish Free State in 1922, and formally confirmed as the National Flag in the 1937 Constitution under Article 7:

The national flag is the tricolour of green, white and orange.