[4][1] According to historian Paul Walsh, "Conn O'Neill is commonly believed to have been Tyrone's youngest son; but he was seven or eight years old in 1609 and consequently born before Brian".

[1] Historian Jerrold Casway corroborates this with his statement that Conn was five years old at the time of the Flight of the Earls,[9][10] which occurred in September 1607.

[5][11] Conversely, Charles Patrick Meehan believes that Conn was seven years old at that time, meaning he would be born around 1600.

[12] In a letter to Dublin's Privy Council dated 4 July 1609, Chichester suggested that the children of former Irish confederacy members should be sent to England and put to trades, so that they might "forget their fierceness and pride."

Chichester declared that the best course would be "to send [the children] to some remote parts of England or Scotland to be kept from the knowledge of friends or acquaintances.

[citation needed] However, Conn quickly became the focus of plots to make him the figurehead of an uprising, notably the Ulster Conspiracy of 1615.

[2] Allegedly, a goal of the conspiracy was "to take away Conn ne Kreigy O Neile, son to the Earl of Tyrone, from Charlemont.

King James I already planned to have "the sonnes of divers noblemen and gentlemen" of Ireland sent to England to be raised in the English manner.

[20][15][2] In response, Tyrone stated that "a son of mine is even now being reared in heresy, but I trust in God that the blood he has in his veins will not permit such a deception, and that one day he will avenge me for this outrage".

[26] His father died in Rome in July 1616,[5] and Conn's elder brother Shane was recognised by the Spanish as the successive Earl of Tyrone.

[20] Conn was held in the Tower with a number of his relatives of the O'Neill and O'Donnell dynasties and may have lived in some comfort as was common for a nobleman.

[15] Historians Jerrold Casway and John McGurk believe Conn died in the Tower,[28][19][11] most likely from starvation and neglect.