Conn was the son of Calvagh O'Donnell, ruler of Tyrconnell. Calvagh had positioned his branch of the O'Donnell dynasty, settled at Lifford, as friendlier to Crown interests than that of Hugh mac Manus, who had rendered himself suspicious by his alliance with the rebellious Shane O'Neill. Calvagh had been considered several times for elevation to the peerage as Earl of Tyrconnell, although this was never put into effect. Conn spoke English as well as the Irish language, probably as a result of fosterage under Sir Thomas Cusack. Conn attempted to follow much the same policy as his father, being described by the Lord DeputyThomas Radclyffe as "the likelyest plante that ever sprange in Ulster to graffe a good subject on." The earliest mention of Conn is in 1557 when he participated in a daring night time raid at Balleeghan, Co. Donegal which halted a campaign undertaken by Shane O'Neill and Hugh mac Manus O'Donnell to undermine the leadership of Calvagh.
Factional leader
In 1561, Calvagh was betrayed by a cabal of his subjects and captured by Shane O'Neill, after which Conn assumed effective leadership of the Lifford faction of the O'Donnell dynasty. Initially, Conn sought Crown assistance to release his father. But in 1562 Conn allegedly entered into an agreement with Shane by which Conn would consent to the continued imprisonment of his father in exchange for safe possession of his father's estates. However, in May 1564 Conn found himself in Shane's captivity as a result of a failed attempt to oust from Donegal Castle his great uncle, Hugh mac Hugh Dubh Óg, a partisan of his rival, Hugh mac Manus O'Donnell. Shane released Conn in May 1567, at the same time delivering to Conn possession of the castles at Ballyshannon and Belleek, which were traditionally considered perquisites of the lordship of Tyrconnell that rightfully belonged to Hugh mac Manus since the latter's election in 1566 to succeed Calvagh in that office. The conflict seems to have been temporarily resolved by mutual agreement before 30 October 1567, when Conn was made tanist to Hugh mac Manus. In early July 1568 Conn raided Armagh town, which at that time was under the authority of the Archbishop of Armagh, whose nomination was controlled by the English Crown. In July 1573 Conn sought rapprochement with the Crown. However, he was imprisoned by the Earl of Essex, allegedly through treachery, in 1574. By Autumn 1575 Conn had escaped and obtained a pardon from the returning Lord Deputy, Sir Henry Sidney. The circumstances of Conn's death are not known.
Family and legacy
Many accounts of Conn's family, probably based on the work of 19th century historian John O'Donovan, state that Conn married a daughter of Turlough Luineach O'Neill. However, the only accounts citing specific contemporary documents state that Conn married Rose, daughter of Shane O'Neill, sometime after 29 September 1562. The confusion may arise from Shane's aggressive behavior towards the O'Donnells and a reference to Conn as "cousin", interpreted wrongly in the broader Elizabethan sense of "relative", to Turlough Luineach. Conn and Turlough most certainly were cousins in the fully modern sense, as Turlough's mother, Rose O'Donnell, was a sister or half-sister of Conn's father, Calvagh. Conn's wife, Rose O'Neill, died in 1585. Conn had four notable sons Niall Garve, Hugh Boy, Donal and Conn Oge O'Donnell. After Conn's death and while these sons were minors, the claim to chieftainship of the O'Donnell clan and lordship over Tyrconnell of this branch of the dynasty was upheld by Hugh "mac an Déagánaigh" O'Gallagher who was presented as a natural son of Calvagh but was probably actually Conn's son-in-law. All traceable branches of the O'Donnell dynasty which are currently known to have survived the 17th century descend from Conn in the direct male line, although these also descend from his rival Hugh mac Manus through female ancestors.
