This Earl, on the resignation of his father, obtained a charter of the Earldom, including the patronage of the Hospital of St.Magnus at Spittal, which was followed in 1480 by a charter of the jurisdiction. In 1478 he or his father was decerned by Parliament to refund to the burgh of Innerkeithen the petty customs of the burgh of Dysart, intromitted with for the space of 17 years. [from Hay's Genealogie].
He joined the confederacy of nobles who hanged Cochran, and the other favourites of James II, at the bridge of Lauder, in 1481; and on the second rebellion of the barons in 1488, headed by the kings own son, he appears to have allied himself to the royal cause, as well as Huntly, Crawford, and many others who had leagued for the destruction of the favourites. Huntly and Crawford fought at Sauchieburn on the king's side, but Caithness appears not to have arrived in time for the battle, although Abercrombie and Holinshed distinctly state that he and others were on their way to the assistance of King James. [From History of Caithness].
This Earl is a party to two ancient charters, one of lands in Caithness, and the other in Shetland. The former was executed at Girnigoe Castle, 14th March 1496, being a charter from William de St.Claro, Earl of Caithness, to John Groat, son to Hugh Groat, of one penny land in Duncansby, paying therefore yearly tres modios Brasii at Martinmas. [From History of Caithness].
The Shetland charter was dated at Edinburgh, the 3rd December 1498, where Earl William, with the consent of his brothers and sisters, disponed the lands of Swinburgh, in the lordship or Shetland. Nisbet, who states he saw this charter, adds: "to which all their seals were appended entire, with their proper differences, that of the Earl being a seal couchy, and quartered first and fourth a ship under sail, second and third a lion rampant, and over all, dividing the quarters, a cross ingrailed; the shield was timbred with a helmet, enseigned with a flower-de-luce for crest; supported on the dexter [right] by a griffin, and on the sinister [left] by a lion, and the legend around the seal Sig. Willielmi Comitis Cathaniae." This instrument, if still extant, might clear up the question of seniority between Earl William and his brother Sir Oliver of Roslin, and might perhaps inform us of other relationships. [From Nisbet's Heraldry].
NOTE - In the Swinburgh charter of 1498 the enumeration is first according to rank and then to seniority in this order: William, Earl of Caithness; Oliver St.Clair of Roslin, knight; Messrs. Alexander, George, Robert and Arthur Sinclare; Eleanor Sinclare, Countess of Atholl; Elizabeth Sinclare, Lady of Houston; Margaret Sinclare, Lady of Balmute; Catherine, Euphemia, Marjorie and Mariota Sinclair. Thus the ex-Duchess of Albany yields precedence to her married sisters.
In 1503 Parliament passed an act saying: "Because there has been great lack and fault of justice in the north parts, as Caithness and Ross, for fault of the want of division of the sheriffdom of Inverness, to our regret, and these parts are so far distant from the burgh of Inverness, through which people cannot come speedily there by reason of the great expense, labour, and travel, and therefore great enormities and trespasses have grown, in default of officers within those parts who have power to put good rule among the people, etc., etc.". On these grounds there was to be a sheriff of Ross and one of Caithness, the latter sitting at Dornoch or Wick as convenient. It is said that this act, though passed, was inoperative till ratified for Caithness in 1641 and Ross in 1649. [From Caithness Events].
At the Parliament in Edinburgh on 8th June 1504, the Earl witnessed a document by the Earl of Atholl promising to underlie the law for treason.
There is a remission cited as made by George Hepburn (uncle of the first Earl of Bothwell), who was Apostle or Bishop of the Isles from 1510 to 1513, in favour of this Earl, "for all murders and crimes committed by him from the year 1501 to 1510". " Murders and crimes" must mean incidents of disputed administration, feuds, and property quarrels, according to the language of the period, not personal felony. In the sasine or possessory document following his son John's retour in 1513, there is this reference to the remission, "Wherein the murder of the Bishop is thought to be comprehended, of date 1510". This ecclesiastical remission was a pre-requisite to that on Flodden Field [Caithness Events] from the Scottish sovereign, who had apprised Canisbay, etc., from him for a debt of £400. This Earl William, the second of the Sinclairs, who held the Earldom of Caithness, resided at Castle Girnigoe, situated on a projecting rock or precipice near Noss Head, on the east side of Sinclair Bay. From the ruins of this castle still standing, it was not only a mansion of great strength, but also, for those days, of considerable architectural elegance. Girnigo was built for strength, and Castle Sinclair for beauty. The old saying runs: -
"Girnigo was Girnigo ere Sinclair's first stone was laid,
And Girnigo will be Girnigo when that Sinclair is dead."
He was married to the Lady Mary Keith, daughter to the Laird of Inverugie, Aberdeenshire, afterwards Earl-Marischal of Scotland. The latter was possessed of lands in Caithness, and resided frequently at Ackergill Tower, a very strong keep at the most inland part of Sinclair Bay, about a couple of miles west of Castle Girnigoe. He was possessed of property throughout the whole North of Scotland, and it is said that when he occasionally came from his chief seat of Dunottar Castle, in the Mearns, to visit his estate in Caithness, he could, during the course of his journey, rest every night in a house of his own. [Kennedy Manuscript]
Having quarrelled with his son-in-law, the Earl of Caithness, he took an opportunity, on a New Year's Day morning, when Caithness and some attendants had been out coursing with greyhounds, and were returning on horseback within bowshot of the battlements of Ackergill Tower, to wound him with an arrow, which stuck firm in the back of his neck. Finding himself wounded, the Earl did not attempt to withdraw the arrow, but, having clapped spurs to his horse, arrived at his own house of Castle Girnigoe. His lady enquiring what sport he had met with, be replied, "Not much; only in passing by Ackergill Tower, your father sent home a New Year's gift for you, which you may find fixed in the back of my neck. " [Kennedy Manuscript]
In 1505, the Earl sat in the Scottish Parliament. He began the erection of a large building at Knock Einar, in Caithness, but being called South to join in the Scottish invasion of England, the building was never finished. [From Torfaeus].
He took a prominent part in the Battle of Flodden, being in the right wing, led by the Earl of Huntly, who defeated the English left, but on returning from pursuit found the rest of the Scottish army in sad straits. Of the leaders of the Scottish right, the Earls of Huntly and Sutherland saved themselves by flight, but Gordon of Gight and the Earl of Caithness stood their ground, and at the head of their men gallantly yielded up their lives. Andrew Stewart, Bishop of Caithness, and Lord Treasurer of Scotland, also fell on this unhappy occasion. A French contemporary gazette, in enumerating the killed, has inter alia: "L'Evesque de Katnes; Le Conte de Katnes". [From History of Caithness]
Earl William II married Mary, daughter of Sir William Keith, of Inverugie, by whom he had
WILLIAM, legitimised in 1543, of whose descendants, if any, no account has been discovered. [From Caithness Family History].