Oil on canvas, 124cm by 99cm.
William Cecil was the second son of John, 5th Earl of Exeter (1648-1700).
He was sometimes referred to as William Cecil of Snape, for the Cecil property, Snape Castle in North Yorkshire, which his father had restored after several years of neglect, and where William usually resided.
He died unmarried.
There are several portraits at Burghley by the German-born Kneller.
He was the leading portrait painter in England during the late 17th and early 18th Centuries and court painter to monarchs from Charles II to George I, who knighted him.