No family in Ireland can point to a more ancient pedigree than the Kavanaghs. They can trace it back to the dawn of Irish history. Tradition, indeed, carries it far beyond that limit - to the legendary Feniusa of Scythia, coeval with the Tower of Babel, whose descendants, having wandered into Egypt, found their way back again to Scthia, and thence to Spain, from which country Heber and Heremon, the 2 sons of Gallamhy or Milesius, crossed over to Ireland, reduced it to subjection and divided it between them. From them sprang lines of Kings ruling over the 5 monarchies into which the island was split up.

One branch eventually established themselves as Kings of Leinster and from Murchadh, or Morrough, King of Leinster, in the 11th C, the family became known as MacMorrough. The grandson of this Monarch was Dermot MacMorrough, surnamed, na-nGall, that is, "of the Strangers", who invited the Normas to Ireland in 1167.

Dermot in order to secure the support of Richard de Clare, Earl of Pembroke, surnamed Strongbow, to re-establish himself in his Kingdom, from which he had been expelled, agreed to give him his daughter Aoife in marriage. On the death of Dermot in 1171, Strongbow claimed the throne of Leinster in right of his wife, and in defiance of Irish law and custom. He was soon obloiged to renounce his pretensions to establishing himself as an independent sovereign, and surrendered his rights as such to King Henry II.

Art Mór Mac Murchadha Caomhánach (anglicized Art mac Art MacMurrough-Kavanagh; died 1416/17) is generally regarded as the most formidable of the later Kings of Leinster. He revived not only the royal family's prerogatives but their lands and power. During the length of his forty-two year reign he fully lived up to his title, dominating the Anglo-Norman settlers of Lenister.

His dominance of the province and its inhabitants - both Gaelic and Hiberno-Norman - was deemed sufficiently detrimental to the colony that Richard II spent much of the years 1394-1395 sparring with him. While Art did indeed submit to Richard, he renounced this fealty on Richard's departure and made much of his kingdom a death-trap for any invading English or Anglo-Irish forces. He was very much cut of the same cloth as his ancestors Diarmait mac Mail na mBo and Diarmaid Mac Murchadha.