Owen MacCarthy Reagh (Irish: Eoghan Mac Carthaigh Riabhach) (1520–1594) was the 12th Prince of Carbery from 1576 to 1592. He belonged to the MacCarthy Reagh dynasty. Owen was commonly referred to as "Sir" Owen MacCarthy (McCartie) in the English court records. He surrendered the MacCartie clan lands for regrant in 1606.
Owen was the fourth son of Donal MacCarthy Reagh, 9th Prince of Carbery (r. 1505–1531) by his wife Lady Eleanor, daughter of Gerald FitzGerald, 8th Earl of Kildare, Owen became tánaiste in 1567, when his next elder brother Donogh MacCarthy Reagh, 11th Prince of Carbery (r. 1567–1576), father of Florence MacCarthy, succeeded their elder brother Cormac na Haoine MacCarthy Reagh, 10th Prince of Carbery (r. 1531–1567).
He was succeeded by the son of his brother Cormac na Haoine, Donal of the Pipes, 13th Prince of Carbery.
Owen did not support Gerald FitzGerald, 15th Earl of Desmond during the Second Desmond Rebellion. Instead he allowed his forces of around 1200 fighting men to be employed by the Crown, and thus prevented much of the destruction that Carbery might have suffered if he had supported FitzGerald. He was accused of joining the rebellion in 1580, and may have given the appearance of it, but his friend Thomas Butler, the Earl of Ormond, prevailed upon him to cease whatever activity and convinced the government it was only local politics. MacCarthy Reagh's difficulties with the Crown's sub-sheriffs are suggested as the cause.
The total size of MacCarthy Reagh's forces is more difficult to determine. According to one count this included a peacetime 1,000 infantry and 30 knights, but according to another in 1588 his private forces greatly exceeded this, amounting to 60 horsemen, 80 professional soldiers, and 2,000 light infantry.