The kings of Osraige (alternately spelled Osraighe and Anglicised as Ossory) reigned over the medieval Irish kingdom of Osraige from the first or second century AD until the late twelfth century. Osraige was a semi-provincial kingdom in south-east Ireland which disappeared following the Norman Invasion of Ireland. A number of important royal Ossorian genealogies are preserved, particularly MS Rawlinson B502, which traces the medieval Mac Giolla Phádraig dynasty back through Óengus Osrithe, who supposedly flourished in the first or second century. and one in the Book of Leinster (also known as "Lebor na Nuachongbála"). Recent analysis of ninth and tenth century regnal succession in Osraige has suggested that in peaceful times, kingship passed primarily from eldest to youngest brother, before crossing generations and passing to sons and nephews.

Early kings of Osraige

The following kings are listed in all major genealogies, but originate from an early period in Irish protohistory, and likely stem from oral tradition.

Kings of Osraige to 1103

The following is a synchronism of the kings of Osraige from historic times until the death Gilla Patraic Ruadh in 1103, after which the kingdom experienced some political fracturing.

Kings of Osraige from 1103 to the Norman Invasion

Upon the death of king Gilla Patráic Ruadh in 1103, two smaller portions of the kingdom broke away from the central polity of Osraige; the area of Mag Lacha in the far north of Osraige became independently ruled by the Ua Caellaide clan, and Desceart Osraige ("South Osraige") in the very southern area of Osraige, ruled intermittently by rival members of the Mac Giolla Phádraig clan.

Kings of Osraige from the Normans to the Tudors

The kingdom of Osraige did not fully disappear after the arrival of Norman mercenaries in Ireland, though it was greatly reduced in size. The lineage of Osraige's Lords remained in power in the northern third of their original territory, having been pushed back through the arrival of William Marshal who sought to consolidate his wife's huge claim to Leinster, including Osraige. The lords who ruled this area were sometimes also known in the annals as ‘Princes of Osraige’, ‘Kings of Upper Osraige’ (or ‘North Osraige’), or ‘Kings of Slieve Bloom’; it was a period when the concept of Irish ‘Kingship’ was being replaced with ‘Lordship’. They generally maintained their independence from the Crown or any shire until the final submission of Barnaby McGillaPatrick in 1537 and his subsequent conversion to the title of 1st Baron Upper Osraige in 1541, however, from the mid 1400s to the early 1500s they were at times in alliance with the House of Ormond as well as the House of Kildare. Fitzpatrick historians such as Carrigan and Shearman could not, in their day, access all available records, and their interpretations of succession are often confusing and ambiguous. The following list may include powerful members of different lines of the family, who may or may not necessarily have been inaugurated as the Mac Gilla Pátraic per se, but who were likely recognized nonetheless as the de facto ruler or potential heir, and noteworthy enough for reference by the annalists and in key records such as Liber Ruber, the Ormond Deeds and the Kildare Rental.