Devaynes was baptised at St Martin-in-the-FieldsWestminster25 October 1730. He was the fifth of six children baptised there for Huguenot peruke maker John Devaynes and his wife Mary, only surviving child of London's City Remembrancer, William Barker. An elder brother, John Devaynes, was apothecary to King George III and Queen Charlotte from 1761 to 1795. He appears in Boswell's Life of Johnson as "that ever-cheerful companion Mr Devaynes, apothecary to his Majesty" and was the Devaynes of Messrs Devaynes & Hingeston, court apothecaries, married to Juliana sister of Chambre Hallowes, son-in-law of Edward Lovett Pearce. His first wife, Jane Wintle, provided a daughter and a son also William Devaynes, born September 1783, who had children but died just 12 months after his father, 8 December 1810, aged 27. Mary Wileman, his second wife whom he married 3 February 1806, was said to be 60 years younger than he was. He is reported to have made a settlement on her by which it was in her interest to keep him alive as long as she could and that proved to be almost four years. He died 29 November 1809 in his 80th year. Years later on 13 April 1813 at Marylebone Mary married SerjeantThomas Wilde who late in life was made Lord Chancellor and 1st Lord Truro. She bore Wilde a daughter and two sons. Devaynes was also survived by an illegitimate daughter and grandson, William Devaynes of Liverpool.
Africa
He was a director of The African Company of Merchants. During Parliament's discussion of the slave trade Devaynes made various statements about West Africa: It seems he spent his early years in Sierra Leone; in his will he made provision for a mulatto daughter.
Banker
Banking was his core occupation. After he had risen to senior partner his firm, which operated from 39 Pall Mall, London, was known as Devaynes, Dawes and Noble. Devaynes died a rich man. However his estate remained a partner in the bank and a year after his death his banking house was bankrupt. Consequential litigation involving his heirs was to persist for 30 years after his death.
Clayton's case
Part of the litigation gave rise to the rule in Clayton's case still commonly applied in the 21st century arising from the judgment by Sir William Grant in Devaynes v Noble. Devaynes in this case was the son 1783-1810 and Noble was his father's former partner in the bank. Clayton was a depositor of the failed bank who hoped for funds from the deceased partner's estate.
India
Devaynes was active in the East India Company being chosen by his fellow members of the court of directors to be chairman five separate years. He was a friend of Warren Hastings.
