Bentley, born in Hampstead, London, was the youngest of his parents' nine children. His father was retired businessman Alfred Bentley, and Adelaide-born mother was Emily, née Waterhouse. As the son of a prosperous family, he was privately educated at Clifton College in Bristol from 1902 until 1905, when at the age of 16 he left to start work as an apprentice engineer with the Great Northern Railway at Doncaster in Yorkshire.
The premium five-year apprenticeship with Great Northern, which cost his father £75, taught W.O. to design complex railway machinery and also gave him practical experience in the technical procedures to cast, manufacture, and build it. He completed his apprenticeship in the summer of 1910 but decided that the railways did not offer him enough scope for a satisfying career. Afterwards, he studied briefly theoretical engineering at King's College London.
In 1912 W.O. Bentley and his brother H.M., with their newly formed company Bentley & Bentley Ltd., which was specialised in selling the D.F.P cars (Doriot, Flandrin & Parant (D.F.P.) was a French car maker based in Courbevoie, Seine between 1906 and 1926). W.O. Bentley and his brother H.M., had acquired the British and Commonwealth Agency for the French-built Doriot, Flandrin et Parant motor cars.
During World War I, he was a Captain in the Royal Naval Air Service, where he played a major role in improving the design and manufacture of Clerget engines for the Sopwith Camel and the Sopwith Snipe aircraft. These were known as the BR1 (Bentley Rotary 1) and BR2 and were made by Humber. For this he was awarded an MBE (Member of the Most Excellent Order of the British Empire), and an award of £8,000 from the Commission for Awards to Inventors.
In January 1919, Almost immediately after the end of the First World War, W.O. and H.M. founded their own car company, Bentley Motors Limited. H.M. and W.O. Bentley and H.M.J. Ward are listed as directors. In October of the same year the first Bentley is completed. The 3-litre is built in a workshop near Baker Street, London, and powered by a 65bhp four-cylinder 16-valve engine. The car is the first to carry Bentley's hallmark radiator casing and Flying 'B' insignia.
In May 1923, John Duff and Frank Clement drive a privately-entered 3-litre to fourth place in the first 24-hour Le Mans race. One year later, the two drivers won Bentley the first Le Mans. However, the next endurance race was a disaster, while Bentley Motors Limited was in serious financial difficulties. Nevertheless, the victory at Le Mans convinced Woolf Barnato to help the company with its financial problems. The company was saved, however, W. O. was no longer a co-owner of the company but Barnato's employee.
In November 1931, with Barnato refusing to continue to finance the company and Bentley with a Receiver, Bentley was sold to the British Central Equitable Trust which was purchasing for Rolls-Royce. W.O. continued to work for Bentley after his former company was acquired by Rolls Royce but he was unhappy and left in 1935 when his contract expired.
In 1935, the Lagonda car company was bought by Alan P. Good, who outbid Rolls-Royce. He also persuaded W. O. Bentley to join Lagonda. He continued to work for Lagonda with Bentley touches to the engines.
W. O. Bentley died at the Nuffield Nursing Home, Woking, on 13 August 1971.
According to myautoworld.com and en.wikipedia