In the same year, 1498, he was one of three commissioners appointed to assess fines on those who had taken part in the revolt on behalf of Perkin Warbeck in the previous year in Devon and Cornwall. He was also one of three appointed for a like purpose (but apparently two years later) for the counties of Somerset, Dorset, Wiltshire, and Hampshire, and he had a special commission to himself to execute the offices of constable and marshal of England on those who refused to compound. On 6 July 1499 he was appointed one of five ambassadors to settle disputes with Scotland. Besides being captain of Berwick, he was on 10 September 1501 appointed treasurer and chamberlain of that town, and customer of the port there. In the latter part of the year 1502 he and Henry Babington were despatched into Scotland to receive the oath of James IV to a treaty of peace, which they accordingly did at Glasgow on 10 December.
Shortly before this, in 1499/1500, he was appointed by the crown constable and steward of Sheriff Hutton; and afterwards, on 12 July 1503, receiver-general of the lordships, castles, and manors of Sheriff Hutton, Middleham, and Richmond in Yorkshire. On 8 June 1505 we first find him named Lord Darcy in a patent by which he was made steward of the lands of Raby and other possessions of the young Earl of Westmorland, then a minor. These offices, together with his new peerage, must have given him an influence in the north of England second only to that of the Earl of Northumberland, when on 1 September 1505 he was appointed warden of the east marches, a higher office in dignity than he had yet held, though he had discharged its duties before as deputy to another.
In 1508 he was one of fifteen lords bound by the treaty for the marriage of the king's daughter Mary with Charles of Castile (afterwards the Emperor Charles V) that that marriage should be completed when the bride came to marriageable age. He was also one of the witnesses of the celebration of the match by proxy at Richmond on 17 December following. Just after the accession of Henry VIII in the following spring he was made a knight of the Garter. He was installed on 21 May. Some changes were then made in his appointments and he gave up the constableship and stewardship of Sheriff Hutton, which were given to Sir Richard Cholmeley in his place. But most of the others were renewed, especially his commission as warden-general of the east marches, and also as captain of Berwick. For these and a number of other offices new patents were granted to him on 18 June, 1509, on which day he was also appointed warden, chief justice, and Justice in Eyre of forests beyond Trent. He was also named of the king's council, and when in London he took part in its deliberations, and signed warrants as a privy councillor. His name stood first in the commission of array for Northumberland; and when the bridge at Newcastle upon Tyne had to be repaired it was to be done under the supervision of Darcy and the prior of Durham.
Soon after his return, on 20 October 1511, he was appointed warden both of the east and middle marches against Scotland, which office, however, he resigned in or before December, when Lord Dacre was appointed warden in his place. In 1512 and 1513 he wrote to the king and Wolsey important information of what was doing in Scotland and upon the borders. In the summer of 1513 he accompanied the king in the invasion of France, and was at the siege of Thérouanne. In January following he writes from his own house at Templehurst an interesting letter to Wolsey, in which he speaks of having recovered from recent sickness, says that his expeditions to Spain and France had cost him £4,000 in three years and a half, but declares his willingness to serve the king beyond sea in the following summer. He reminds Wolsey (whose growing influence at this time was marked by everyone) how they had been bedfellows at court and had freely spoken to each other about their own private affairs, and how Wolsey when abroad with the king in the preceding year regretted that Darcy had not been appointed marshal of the army at the beginning of the campaign.
In 1523 he took an active part in the war against Scotland, making various raids on the borders with a retinue of 1,750 men. In the same year he obtained a principal share in the wardship of the son and heir of Lord Monteagle, which led to many complaints from one of the executors named Richard Bank. On 12 February 1525 he was again appointed to conduct a privy search at Stepney. The annual revenue of his lands in various counties is given in a contemporary document as £1,834 4s., and he was taxed for the first and second payment of the subsidy at no less than £1,050.
He was one of the peers who signed the articles prepared against Wolsey in parliament on 1 December, partly founded on the charges drawn up by himself five months before; and in the following year he signed the memorial of the lords spiritual and temporal of England to Pope Clement VII, warning him of the danger of not gratifying the desire of Henry VIII in the matter of the divorce.
Among matters of minor interest about this period we find him reminding Bishop Tunstall after his promotion to Durham of a promise of the offices of steward and sheriff of his bishopric. A long-standing dispute with his neighbours at Rothwell in Yorkshire comes to light in a commission obtained in April 1533 to examine certain of the inhabitants who had threatened, in defiance of a decree of the Chancellor of the Duchy of Lancaster, to pull down the gates and hedges of Rothwell park.
In July 1534 he was one of the jury of peers who acquitted Lord Dacre, an act which was scarcely calculated to make him more acceptable to the court. Cromwell, however, appears to have been his friend, and obtained for his second son, Sir Arthur Darcy, the office of captain or governor of Jersey in September following, for whose appointment he wrote Cromwell a letter of thanks from Mortlake, regretting that he was unable to visit him personally, owing to his 'fulsum diseassis.' It appears that he was suffering from a rupture. He at the same time sent Sir Arthur with messages both to Cromwell and to the Duke of Norfolk, among other things complaining that he had not been allowed to go home into Yorkshire since the parliament began. And this must mean since November 1529 when the still existing parliament began, not since the beginning of a session, for it was then vacation time. A significant part of the instructions to Sir Arthur as regards the Duke of Norfolk was to deliver a letter to him 'for no goodness in him but to stop his evil tongue'.
For these important privileges he writes to thank Cromwell on 13 November, dating his letter from Templehurst, where, however, he could hardly have been at that time, as Chapuys expressly says on 1 January 1535 that he had not yet been allowed to retire to his own country. The hope of soon going home to Templehurst seems to have influenced his pen to write as if he were actually there when he really was in or about London. The fact is that, although these exemptions were conceded to him on the ground of age and infirmity, permission to go back to his home in Yorkshire was still persistently withheld. The court apparently suspected that his presence in the north would do them little good, and he remained not only till the beginning of 1535, but through most part of the year, if not the whole of it. He kept up secret communications with Chapuys at intervals in January, March, May, and July, hoping now and again that matters were ripe for a great revolt, and sending the ambassador symbolic presents when he dared not express his meaning otherwise. In the beginning of May he was hopeful at last of being allowed to go home immediately. But in the middle of the month, this hope having apparently disappeared, he was thinking how to escape abroad and endeavour to impress upon the emperor in a personal interview the urgent necessity of sending an expedition against England to redeem the unhappy country from the heresy, oppression, and robbery to which it was constantly subjected. How long he was detained in London we do not know, but it was certainly till after July. He appears to have been at Templehurst in April 1536; but there is a blank in our information as to the whole preceding interval.
His presence not being required in the parliamentary session of February 1536, he escaped the pressure which was doubtless brought to bear upon others to vote for the dissolution of the smaller monasteries, a measure which was very unpopular in the north of England, whatever it might be elsewhere. This, indeed, was one of the chief causes of that great rebellion which, beginning in Lincolnshire in October following, soon spread to Yorkshire, and was called the Pilgrimage of Grace.
Almost the only place which seemed for a time to hold out against the insurgents was Pontefract Castle, of which Darcy held the command. Thither fled Archbishop Lee of York, who put himself under Darcy's protection with some of the neighbouring gentry. But Darcy, pretending that his provisions had run short, yielded up the castle to the rebels, who compelled him and the archbishop to be sworn to the common cause. The compulsion, however, was more ostensible than real. Darcy, the archbishop, and nearly all the gentry, really sympathised with the insurgents, and it was in vain that Darcy afterwards pleaded that he was doing his utmost for the king by endeavouring to guide aright a power that he could not resist.
He stood by Robert Aske, the leader of the commons, when Lancaster Herald knelt before him, and he negotiated in their favour with the Dukes of Norfolk and Suffolk when they were sent down to suppress the rising. His position as a friend and leader of the insurgents was recognised by the king himself, who instructed Norfolk and Fitzwilliam to treat with him as such, and authorised them to give him and the others a safe-conduct if necessary, to come to his presence, or else to offer them a free pardon on their submission. Both he and Aske wrote to the king to set their conduct in a more favourable light. A meeting with some of the king's council was arranged at Doncaster, and the king sent a pardon even to the chief offenders. But on 6 January following (1537) Henry sent him an imperative summons to come up to London; in reply to which he wrote from Templehurst on the 14th, stating that he had 'never fainted nor feigned' in the service of the king and his father within the realm or abroad for about fifty years; but since the meeting at Doncaster he had been confined to his chamber with two diseases, rupture and flux, as several of the council who saw him at Doncaster and the king's own physicians could bear witness.
The country was at that moment in a very dangerous state, a new rebellion having been just begun by Sir Francis Bigod, which Aske and Darcy did their best to stay. Their services were so real that the king pardoned both of them, and encouraged Darcy to victual Pontefract, that his two sons, Sir George and Sir Arthur, might keep it in case of a new rising. Darcy was further assured, by letters addressed to the Earl of Shrewsbury, that if he would do his duty thenceforward it would be as favourably considered as if he had never done amiss. Encouraged by this he wrote to Aske on 10 February, asking him to redeliver secretly to Pontefract Castle (for the custody of which Darcy was responsible) all the bows and arrows that he had obtained out of it. The letter unluckily was intercepted, and it told a tale.
Information was collected to show that since his pardon Darcy had been guilty of different acts of treason, among which his intimating to the people that there would be a free parliament to consider their grievances was cited in evidence that he was still seeking to promote a change, and that if there were no parliament the rebellious spirit would revive with his approval. Even his recent acts in the king's behalf were construed to his disadvantage; for having given orders to stay the commons till Norfolk came, the words were taken to imply that he only wished them pacified for a season.
They were condemned to suffer the old barbarous penalty of treason, but the punishment actually inflicted upon them was decapitation, which Lord Hussey underwent at Lincoln, whither he was conveyed on purpose to strike terror where the insurrection had begun. But Darcy was beheaded on Tower Hill on 30 June. His head was set up on London Bridge, and his body, according to one contemporary writer, was buried at Crutched Friars. But if so, it must have been removed afterwards; at least, if a tombstone inscription may be trusted, it lies with the bodies of other Darcys in the church of St Botolph's Aldgate.