A vassal of Hugh O'Neill, Earl of Tyrone, O'Cahan was frequently in rebellion alongside his lord in the closing years of the 16th century.
Although he did not go into exile with Tyrone, he claimed to have been betrayed by the English Crown, which he accused of failing to keep to an agreement over a large grant of lands.
[7] In 1607, with English authorities turned against Tyrone, George Montgomery, the new Protestant Bishop of Derry, encouraged O'Cahan to leave Rose and return to his first wife.
[1] The antiquarian Francis Joseph Bigger has suggested that he was rumoured to have attempted flight with Tyrone and the other rebel lords, and had only been prevented from doing so by an "accidental delay in crossing some ferry on the road".
[2] This was compounded by the fact that, in English eyes, O'Cahan "had become troublesome, and almost unmanageable of late, so, everything considered, it was thought best to take him also into special keeping at Dublin Castle".
[15] Bigger notes that, although O'Cahan had remained loyal to his liege lord throughout the latter's seven-year campaign at the Crown, in 1608 he joined the major English statesman and commander in Ireland, Henry Docwra, on condition that O'Cahan would receive sufficient grants and lands to enable him to establish himself independently of Tyrone, and would no longer hold his estates in fief.