We are grateful to Caroline Pegum of the National Portrait Gallery, London for confirming the artist as Charles Jervas.

Henrietta Pelham-Holles was the wife of the British Prime Minister Thomas Pelham-Holles, 1st Duke of Newcastle-upon-Tyne. She was the daughter and co-heir of Francis Godolphin, 2nd Earl of Godolphin and the granddaughter of Sidney Godolphin, 1st Earl of Godolphin and Sarah and John Churchill, 1st Duke of Marlborough. Until her marriage in 1717 she was known as Lady Harriet Godolphin. With her husband she was an active Whig and supporter of the Hanoverian succession. The Duchess died on the 17th of July 1776 and was buried alongside her husband at Laughton. 

Charles Jervas was born in Ireland in 1675. He trained under Godfrey Kneller in London and in Rome, returning to London in 1709 establishing a successful portrait practice before becoming Painter to King George I after Kneller's death in 1723. Both Henrietta and her husband had their portraits painted by Jervas (National Portrait Gallery, London). His sitters also included intellectuals of the day such as friends Jonathan Swift and Alexander Pope (National Gallery, London). Jervas lived in London until his death in 1739.