Manning was born on 20 October 1879 at Staines, Middlesex the son of Herbert Lane Manning and Alice Allenby Manning (née Richardson). He was educated at St Paul's School, London and served as an apprentice with Callender's Company. He became an electrical engineer and in 1907 or 1908 he met Howard T. Wright, who had a firm dealing with electricity generating installations and had built some early aircraft. Manning and Wright both had an interest in aviation and Manning joined his firm in December 1908.

The company soon established itself as a leading aircraft constructor in the United Kingdom and Manning became the Chief Designer. However, by 1911 business had declined and production of aircraft had ceased. Wright sold his aviation interests to the Coventry Ordnance Works, with Manning moving to the new company, where he continued to design aircraft, including the two biplanes for the War Office Aeroplane Competition in 1912.

Following the outbreak of World War One, Manning left Coventry Ordnance and was commissioned as a Lieutenant Engineering Officer in the Royal Navy Volunteer Reserve on 27 November 1914. He was posted to the Royal Naval Air Service experimental base at Port Victoria, then in September 1916 he moved to the Bradford works of the Phoenix Dynamo Manufacturing Company as technical representative for the Admiralty, the company having a number of contracts to build aircraft for the Royal Naval Air Service. Learning of Manning's background, he was approached to be chief designer for the company, whereupon he was released by the Admiralty on 5 October 1916 to take up the position.

Manning's first design for Phoenix was the unbuilt P.1 pusher seaplane. In November 1917 the company was awarded a contract to design an experimental flying-boat, which was to become the Phoenix P.5 Cork. With the completion of the order, it was decided to close the aviation department, though Manning continued with his design work, particularly an idea for a civil flying boat which he named the Eclectic.

With the lack of work caused by the end of the First World War a number of companies including Phoenix merged in December 1918 to form English Electric, with Manning appointed chief aircraft designer of the new concern. At first interested in designing civil flying boats, he soon produced the M.3, a three-seat coastal patrol flying boat and expanded his design team.

In October 1922 Manning was invited to a gliding competition at Itford on the Sussex Downs. This inspired him to look at designs for a very small single-seat monoplane that could be powered by a motor-cycle engine. The first of three Wrens flew on 5 April 1923.

With the closure of English Electrics' aviation department in 1926, Manning was made redundant. From about 1927 to 1929, he became a consultant to FIAT in Italy with the design of racing seaplanes. On returning to the United Kingdom, he took a similar position with Simmonds Aircraft Ltd, of Weston, Southampton, until the company went out of business in late 1935.

From 1935 to 1939 he ran the Airworthiness Department of the British Gliding Association before moving to the Royal Aircraft Establishment at Farnborough. He later moved to Flight Refuelling Limited where he was co-inventor of a probe-mounted refuelling valve. He retired in 1946.

William Oke Manning died at Farnham in Surrey on 2 March 1958.

1. English Electric Aircraft and their Predecessors, Stephen Ransom and Robert Fairclough (Putnam, 1987)