Barclay was the son of David Barclay (1580–1660), 11th of Mathers, of Kincardineshire, Scotland and Elizabeth Livingstone, daughter of John Livingston of Dunipace.[citation needed]
In 1648, he purchased the lands and barony of Ury in Kincardineshire (modern-day Aberdeenshire) from William Keith, 7th Earl of Marischal. As a known associate of the Earl Marischal he was subsequently confined in Edinburgh Castle where he met the John Swinton, who was confined in the same prison.
ODNB article by Brian M. Halloran, "Barclay, Robert (1611/12–1682)", Oxford Dictionary of National Biography, Oxford University Press, 2004, accessed December 3, 2007.