He was best known as the managing director of Dorman Long and the main supervisor of the construction of the Sydney Harbour Bridge.
[4] He was educated at Gavieside School, but due to his family's poor circumstances he left at the age of 12.
[6] Ennis developed his reputation when he patented a new angle iron whilst employed at the Carnegie steel works in Pittsburgh.
[2] Ennis joined Dorman Long in 1903 as superintendent in charge of bridge and constructional works.
[8] Ennis was appointed OBE in 1918, in recognition of his conversion of the Dorman Long works into a munitions manufacturing site during World War One.