William Rowan was born in Mullans, County Antrim, and in 1803 joined the 52nd Foot Regiment. He, like his brother Charles, served during the Peninsular War and took part in the famous charge against the Imperial Guards at Waterloo. In 1856 he was awarded the Grand Cross of the Bath. He became a major general in 1877, and was made a field-marshal. He died in Bath.