Elizabeth Moubray was the daughter of Robert Moubray of Castlelaw, Midlothian, and his wife Catherine Lind. She married a Glasgow merchant, Robert Boyd.
Philip Mercier was born in Berlin, the son of Philippe Mercier, a Hugenot tapestry weaver at the city's royal factory. He studied at the Akademie der Künste and under the court painter to Frederick I of Prussia, Antoine Pesne. In 1716 he moved to London, recommended from the Court at Hanover (Vertue, Note Books, 3.37). In London, Mercier established a successful portrait practice, and by 1729 was appointed as the principal painter to the Prince of Wales, as well as page of the bed chamber, and library keeper.
In October 1736, Mercier left the Prince's service, and lived for a short time in Northamptonshire and then Covent Garden, before settling in York by 1739, where he was extensively patronised by the northern gentry. In 1751 Mercier returned to London with his family, and continued to paint portraits, such as The Burton Family (Paris, Louvre), as well as various single figure genre scenes engraved by Richard Purcell.