Sir William Henry Cowan (22 May 1862 – 11 January 1932) was a politician in the United Kingdom.
The son of William Cowan and Elizabeth Giles, he was educated at Merchiston Castle School, Edinburgh Collegiate School and the University of Edinburgh.
He was elected as Liberal Member of Parliament (MP) for Guildford from 1906 to 1910 and for Aberdeenshire Eastern from 1910 to 1922, then as a Unionist for Islington North from 1923 to 1929. As a parliamentarian, Cowan became interested in matters concerning immigration including promoting immigration of British families to dominions such as Australia.
As of 1928, he was chairman of Parkinson and W. and B. Cowan, Limited, a manufacturer of gas meters and gas cookers.
He was knighted in the 1917 Birthday Honours.