[3] His father lost land after defeat at the Siege of Kinsale, leaving O'Neill to inherit a small estate at a young age in 1619.
[2] According to Clarendon, O'Neill had spent many years between the court and Low Countries, "the winter season in one and the summer always in the army in the other; as good an education towards advancement in the world as that age knew".
[2] His uncle Owen Roe O'Neill was fighting there for the Spanish and D'Alton claims Daniel kept him abreast of affairs at home.
After a summer probably fighting in the Low Countries,[5] Daniel swore the oath of allegiance[10] and was granted a pass "to go beyond the seas" with two servants in December 1636.
[14] In 1638 Wentworth wrote to His Majesty describing O'Neill as a "vey slight and busy person" who was very conversant at Thomas Howard's Arundel House and dependent (for an annuity of £400[13]) on the Earl of Antrim, Randal MacDonnell.
[15] O'Neill was captain of a troop of horse, "to which he was by all men held very equal, having had good experience in the most active armies of that time, and a courage very notorious".
At the Battle of Newburn on 28 August 1640, Conway was ordered by Wentworth (now Earl Strafford) to prevent Leslie's army crossing the river, despite being outnumbered 4 to 1.
His part association with the Palatinate family gave him good standing with the prince, who appointed him as a lieutenant colonel, commanding his own cavalry regiment.
He subsequently fought at Chalgrove Field, where he killed the Parliamentarian standard bearer, regaining honours for his regiment they had lost at the Battle of Hopton Heath.
[22] After failing to secure negotiations in the Irish Confederate Wars, O'Neill went on to serve as a spy to the de jure Charles II at The Hague.
[24] This grant included a £2,000 advance to build gunpowder mills and stove houses, and to annually import 240 tons of saltpetre duty-free.
[25] O'Neill had no experience in gunpowder manufacture and in December 1660 he awarded 2½ year contracts to James Lloyd at Wandsworth and Thomas Carter at Bedfont to produce 480 barrels per month.
[27] A proclamation was made that none but O'Neale [sic] were permitted to carry or deliver letters and postmasters had, upon pain of dismissal, to provide a certificate of conformity from the Church of England within six months.