He sat as a Baron of Parliament on the 14th January 1488, and on the 4th December 1488. Confirmation issued to Henry, Lord of St.Clair, and Margaret, his spouse, for the lands of Cousland, house and fortalice, and Ravenscraig, and adjacent lands, viz., Woolston, Carberry, and Dubbo.
Notices of this Baron in connection with the Orcadian dominions are of frequent occurrence. On the 6th August 1485, he granted an annuity to the Bishop of Orkney, he being then Tacksman [Leaseholder] of those Isles, and it was probably by his influence that an Act of the Scottish Parliament in 1503 to annul all foreign laws within the realm was so altered as to spare the native laws of Orkney and Shetland. [Balfour's Memorial]
There are in existence copies of several of his Rentals of Orkney, extending over a period of from 1492 to 1502, the earliest, prepared in 1492, being known as "My Lord Sinclair's Rental that died at Flodden".
On the 28th May 1489, three grants were issued to him: A 13 years' lease of Orkney and Shetland; the custody of Kirkwall Castle and the fortalices; and the Justiciary, Folderie, and Balliatus for 13 years. On the same day, three precisely similar instruments issued to his brothers-in-law, Patrick, Earl of Bothwell, and John, Prior of St.Andrew's. There are continuous notices of his intromissions for the farms of Orkney and Shetland, viz.: - On the 21st June 1484, per Peter Hakket and Alexander Lask, for the farms of Sanday; in 1488 as Henry Sinclair for Orkney and Shetland; in 1489 the same as Lord of Sancto Claro; in 1491 and 1494 he is arrendatarius; and on the 22nd February 1494, in the Grant of Burray to St.Magnus, he is referred to as "our blood relation Henry Lord Sinclair"; in his 1495 accounts there is a payment to John Sinclair; in 1497 his Island accounts are rendered per Alexander Lask: in those of 1498 Gilbert Kemp and Edward Spittal are named.
There is also a note below of a letter from King James to the Comptrollar and auditouris in which he charges them "to make thankful allowance to our loved cousin Henry, Lord Sinclar": Edinburgh, 10th July in the 3rd year of our reign.
He got a re-grant of the Isles on 1st May 1501, for a period of 19 years, and his accounts for same are duly noted in 1502, 1503, 1506, and 1507. He conveyed Cousland to William, Lord Ruthven, and Isobel, his spouse, confirmation of which is dated 1st July 1493. In 1502 he had sasine to Newburgh and Ythane, and in 1509, as Newburgh had fallen into the King's hands by recognition, he received a new grant, with a license to infeft vassals.
He was created on 13th March 1510, Master of the Artillery, with a fee of £100 a year, which he was allowed to deduct from his Orkney accounts.
His chief residence, Castle Ravenscraig, is one of the best specimens of sixteenth century architecture, and the administration of Orkney and Shetland was probably done by deputies. His account for these lands is one of the simplest of the Rolls, consisting merely of debiting himself with the stipulated rent, and taking credit for rental of the Isle of Burray, which King James created into a Regality in favour of the See of Orkney, and for a few payments in the King's account, chiefly the price of hawks sent from the islands for the royal sport.
The present accounts contain the warrant, dated 15th March 1513, appointing Lord Sinclair "Master of all our Machines and Artillery", with a fee of £100 a year. He was to have meat and drink for himself and eight persons in the King's Hall, and "all other privileges the Masters of Artillery had enjoyed in the past".
Lord Henry seems to have been generally on ill-terms with the inhabitants of Dysart, [Acta Dominorum Concilii] as is shown in 1509 by the complaint of John of Wynde, burgess of Dysart.
In 1512 he was captain of the "Great Michael", the Scottish flagship.
He was a literary nobleman, and it was at his request that his relative, Gavin Douglas, Bishop of Dunkeld, undertook his celebrated translation of the Aeneid into Scottish verse. In the proem to this admirable version, he says that he "took" to translate "this most excellent book"
"At the request of a lord of renown,
Of ancestry most noble, an illustir baron,
Father of books, protector to science and lair,
My special good lord, Henry Lord Sinclare.
Which with great instance, diverse times, sere
Prayed me translate Virgil or Homer,
Whose pleasure soothly, as I understood,
As near conjoint to his lordship in blood !" etc.
Henry, 4th Lord Sinclair married Margaret, daughter of Adam Hepburn, Lord Hailes; and sister of the first Earl of Bothwell, by whom he had -