On 20 January 1465, Thomas Boyd was firstly engaged to Lady Marion Kennedy, youngest daughter of
Gilbert Kennedy, 1st Lord Kennedy, but this marriage did not take place. After his first marriage to Lady Elizabeth Montgomerie, daughter of
Alexander Montgomerie, 1st Lord Montgomerie, he married Princess Mary Stewart, eldest daughter of King James II, before 26 April 1467. Upon their marriage, the
Isle of Arran was given to them as Mary's dowry, and
Law Castle in
North Ayrshire was built for the couple. Being greatly attached to Thomas, his wife Mary later returned to Scotland without him, after he was charged for treason, mainly in hopes of obtaining a pardon for Thomas from her brother King James III. She was however confined at Kilmarnock, and Thomas was summoned to appear within sixty days, which he failed to do so; thus, his marriage to the King's sister was declared null and void, and she was then compelled to marry
James, Lord Hamilton. According to Ferrerius, Buchanan, and other old historians, this took place in 1469, but the correct date was probably February or March 1474. Princess Mary Stewart died apparently about Whitsuntide 1488, having had a son and daughter by both husbands. Thomas Boyd's children by Mary, who were both said to have been born abroad, were: •
James, 2nd
Lord Boyd (1469–1484) killed by Elizabeth Montgomerie's nephew
Hugh Montgomerie, 1st Earl of Eglinton; died unmarried. • Lady Grisel or Margaret Boyd (she is called Grizel in the
genealogies, but appears as Margaret in the Registers of the Great Seal, and in the Papal Dispensation, etc.). She was born between 1468 and 1473, and was married twice: first, to
Alexander Forbes, 4th Lord Forbes, who died without issue before 16 May 1491; and secondly, before 9 August 1509, as the second wife to
Sir David Kennedy, 3rd Lord Kennedy, then created Earl of Cassillis, who died without issue by her at
Flodden on 9 September 1513. By her marriage to Sir David Kennedy, she had no descendants. ==Notes==