How did ancient Irish government function

I don't have time to write out a massive summary as it's such a complicated issue (and it depends what you mean by 'ancient'), and it's more complicated by the fact that most of early Irish history is massively uncertain. I'm also writing this from memory.

The earliest reports of Irish 'government' was the pentarchy of five peoples described around the fifth century: the Ulaid, Mide, Mumu, Connachta and Laigin.

Around the 6th century the Uí Néill family, descendants of Niall of the Nine Hostages, ended up conquering around half of the island by the middle of the 8th century. They seem to have legitimised their rule by creating the title of High King of Ireland and supposedly tracing their lineage back to Conn Cétchathach, a legendary king who was supposedly the first High King. In reality Ireland seems to have been a confederation of minor kingdoms (túatha) under the control of certain families around this point.

The island was at this point broadly divided into two power spheres: the Uí Néill and Connachta in the north claiming descendance from Conn Cétchathach, and the Eoganachta in the south claiming descendance from another legendary king, Mug Nuadat.

By 800AD the Uí Neills had split into two factions ('north' and 'south') but were still the most powerful faction on the island, which was covered in various dynastic túatha. Then the first Viking raids took place, starting a two-hundred-year period of raiding and looting on the Irish coast, and coinciding with major civil wars between the Ui Neills and kings of Munster.

By 859 the Ui Neills had solidified their control over most of Ireland and various annals refer to Máel Sechnaill, then head of the faction, as "King of All Ireland".

The next century or so is largely the various kings of Ireland dealing with Norse settlements on the coast with power shifts between the various clans in Ireland. Then in the early 980s, Brian Boru became the most powerful lord in Munster (south-west Ireland) and entered into conflict with the Ui Neill High Kings. This culminated in his coronation as High King in 1011 - he is recognised as the first ruler in Ireland to have true authority over all the regional kings. Ireland after the death of Brian Boru.

He was killed the next year at Clontarf and the Irish kingdoms largely reverted to being regionalised and independent, with an "interregnum" between 1015-1072.

This confederation with no-one able to claim the High Kingship in earnest was the situation in 1169 when Diarmait Mac Murchada, ousted King of Leinster, asked for help regaining his throne from the Anglo-Norman government in England after the Norman Conquest. There was then a slow crawl over a few years that ended up with Ireland being declared a lordship of the King of England in 1175 (under Irish control) then 1177 (under Norman control).

Norman control of Ireland wasn't really control though: there were sporadic wars over the next 400 years across Ireland, as the majority of Anglo-Normans in Ireland were simply landowners and not the general population. By 1300 they controlled around 70% of Ireland with the famous Ui Neills in the north still hanging on.

There were then a series of feudal reforms over the next couple of centuries, with counties being introduced in 1297 and feudalism (obligations to a lord in return for protection) officially replacing a barter econony and ending the tuatha system that had been the norm.

/r/AskHistorians Thread