Ennis was born in Grimethorpe, near Barnsley in the West Riding of Yorkshire, the son of a coal miner and educated at the Hemsworth Grammar School on Station Road before attending the Redland Teachers Training College near Bristol where he was awarded a Bachelor of Education degree in 1975.
After leaving education he became a raw materials inspector with J. Lyons and Co. bakery at Carlton, before becoming a teacher in 1976 initially at the Elston Hall Junior School in Fordhouses, Wolverhampton.
Ennis was elected to the House of Commons at the 1996 Barnsley East by-election following the death of Terry Patchett.
Following the 1997 general election, Ennis was appointed the Parliamentary Private Secretary (PPS) to the Minister of State at the Department of Health Tessa Jowell, and then in her capacity of Minister of State at the Department for Education and Employment.
[2] Ennis stood as the Labour Party candidate for the North East Ward in the May 2012 Barnsley local council elections.