Irish Australians (Irish: Gael-Astrálach) have played a long and enduring part in Australia's history. Many came to Australia in the eighteenth century as settlers or as convicts, and contributed to Australia's development in many different areas.

There is no definitive figure of the total number of Australians with an Irish background. At the 2006 Census, 1,803,741 residents identified themselves as having Irish ancestry either alone or in combination with another ancestry. This nominated ancestry was third behind English and Australian in terms of the largest number of responses. However this figure does not include Australians with an Irish background who chose to nominate themselves as 'Australian' or other ancestries. The Australian Embassy in Dublin states that up to 30 percent of the population claim some degree of Irish ancestry.

Around 40,000 Irish convicts were transported to Australia between 1791 and 1867, many for political activity, including those who had participated in the Irish Rebellion of 1798, the 1803 Rising of Robert Emmet and the Young Ireland skirmishes in 1848 in the midst of the Great Famine. Once in Australia, many of these prisoners continued to plan escapes from British military custody — for example, the 1804 Castle Hill convict rebellion, and continual tension on Norfolk Island in the same year also led to an Irish revolt. Both risings were soon crushed. In these decades, the Irish language was the main language of Irish prisoners, and many Irish were flogged or killed by fellow convicts for speaking what was seen as a conspiratorial tongue. As late as the 1860s, Fenian prisoners were being transported, particularly to Western Australia, where the Catalpa rescue of Irish radicals off Rockingham was a memorable episode.

The Irish people (Irish: Muintir na hÉireann or na hÉireannaigh; Ulster-Scots: Airisch or Airish fowk) are an ethnic group who originate in Ireland, an island in northwestern Europe. Ireland has been populated for around 9,000 years (according to archaeological studies, see Prehistoric Ireland). The Irish people's earliest ancestors are recorded in legends – they are claimed to be descended from groups such as the Nemedians, Fomorians, Fir Bolg, Tuatha Dé Danann and the Milesians.Lebor Gabála Érenn, a book of Irish mythology tells that Tuatha Dé Dananns were Scythian descendants.

The main groups that interacted with the Irish in the Middle Ages include the Picts, Scots, and the Vikings. Due to this contact, Icelanders are noted for having some Irish descent. The Anglo-Norman invasion of the High Middle Ages, the English plantations and the subsequent English rule of the country introduced the Normans and Flemish into Ireland. Welsh, Picts, Bretons, and small parties of Gauls and even Anglo-Saxons are known in Ireland from much earlier times.