James Sempill was brought up with James VI under George Buchanan, After a course of instruction with the young king, he completed his education at the University of Saint Andrews, and used the title "Mr." or Master on account of his degree, and was also known as "Beltrees" from his family estate.
Sempill assisted James VI in the preparation of his Basilikon Doron. Via James Melville they reached the synod of Fife. Sempill later supported Andrew Melville when he was in 1606 committed to the Tower of London.
Sempill was Ambassador to England in the years 1591-1600 and was knighted on Christmas Day 1600.
Another Scot employed by the King in London, James Hudson, referred to Sempill"s youth and inexperience in May 1599. Hudson added that James Sempill would be "the true Lord Sempill if he had his due."
In August 1599 James Sempill was sent to London to take the place of David Foulis and collect the "gratuity" for James VI, a sum of money which Elizabeth I of England sent to Scotland to support James VI. He became involved in the discussions following the kidnap of Edmund Ashfield by English agent at Leith.
In 1601 he was sent to France, and accompanied the Duke of Lennox from Dieppe to London in October. James Sempill of Beltrees died at Paisley in 1626.
He was on good terms with the Kirk minister Andrew Melville, and caused a furore by showing Melville the contents of Basilikon Doron in advance.
