He succeeded to the title on the death of his father, on 10 December 1559, and during his minority was the ward of Thomas Ratcliffe, third earl of Sussex, for whom he conceived a great friendship.
[1] In July 1574 his refusal, with his cousin Christopher, Viscount Gormanston, to sign the proclamation of rebellion against the Earl of Desmond laid his loyalty open to suspicion, given the tone of the recent papal bull Regnans in Excelsis.
The English Privy Council, thinking that his objections savoured more of 'a wilful partiality to an offender against her majesty than a willing readiness to her service',[3] sent peremptory orders for his submission.
But with Delvin, 'for that he has showed himself to be the chiefest instrument in terrifying and dissuading the rest of the associates from yielding their submission',[5] Elizabeth left it to Sidney's discretion whether he should remain in prison for some time longer.
In the autumn of 1579, Delvin was entrusted with the command of the forces of the Pale, and was reported to have done good service in defending the northern marches against Turlough Luineach O'Neill.
His 'obstinate affection to popery', however, told in his disfavour, and it was as much for this general reason as for any proof of treason that the Anglo-Irish government, in December 1580, committed him, along with his father-in-law, Gerald FitzGerald, 11th Earl of Kildare, to Dublin Castle on suspicion of being implicated in the rebellious projects of Viscount Baltinglas.
[6] He carried letters of commendation to the new lord deputy, Sir John Perrot; and the queen, 'the better to express her favour towards him,' granted him a renewal of the leases he held from the crown.
New Lord Deputy Sir William Fitzwilliam wrote to Burghley that he hoped that Delvin would "throughly performe that honorable and good opynion it hath pleased yr Lp.
To Burghley, who warned him that he was regarded with suspicion, he protested his loyalty and readiness to quit all that was dear to him in Ireland and live in poverty in England, rather than that the queen should conceive the least thought of undutifulness in him.
He led, he declared, an orderly life, avoiding discontented society, every term following the law in Dublin for the recovery of his lands, and serving the queen at the assizes in his own neighbourhood.
However, in 1593 he was appointed leader of the forces of Westmeath at the general hosting on the hill of Tara, and during the disturbed period (1593–7) that preceded the rebellion of Hugh O'Neill, Earl of Tyrone, he displayed great activity in his defence of the Pale.
He obtained permission to visit England in 1597, and in consequence of his recent chargeable and valourous services, he was, on 7 May, ordered a grant of so much of the O'Farrells' and O'Reillys' lands as amounted to an annual rent to the crown of 100/, though the warrant was never executed during his lifetime.
He writes that the viceroy's authority is too absolute; that the institution of presidents of provinces is unnecessary; that justice is not administered impartially; that the people are plundered by a beggarly soldiery, who find it in their interest to create dissensions; that the prince's word is pledged recklessly and broken shamelessly, and, above all, that there is no means of education such as is furnished by a university provided for the gentry, "in myne opynion one of the cheifest causes of mischeif in the realme.