He was the son of George Playfair, Chief Inspector-General of hospitals in Bengal, and Janet Ross of Edinburgh. He married three times: first, in 1846, to Margaret Eliza Oakes; secondly, in 1857, to Jean Ann Millington; thirdly, in 1878, to Edith Russell of Boston, MA. By his first wife he had an only son, George James Playfair, who succeeded him as second baron.
Playfair was a prominent scientist who was made Secretary of Science in 1853, and Postmaster General in Gladstone's first ministry. His first wife was a cousin of Francis Seymour Haden (AMW's son-in-law).
Dictionary of National Biography, Oxford, 2004; Wemyss Reid, Memoirs and Correspondence of Lyon Playfair: First Lord Playfair of St. Andrews, London, 1899.