He was the second son, but first surviving son, of Robert Boyd, the 5th Lord Boyd, 5th Lord Kilmarnock and Margaret Campbell. As eldest son of Robert Boyd, the 5th Lord Boyd, he assumed the lordship upon his father's death in death in 1590.
1568 (13 May) - Fought alongside his father at the battle of Langside for Mary, Queen of Scots.
1590 - Inherited the title Lord Boyd on the death of 5th Lord Boyd
1592 (12 Jan) - Resigned his whole estate to the King. He obtained a new charter thereof, "erecting the same into a free Lordship and Barony, to be called the Lordship and Barony of Kilmarnock" to himself for life, with remainder to his son and heir apparent, Robert, Master of Boyd, in tail male, remainder to "heirs male," thereby excluding the heirs general. Under this grant Thomas, not improbably, became Lord Boyd of Kilmarnock