Ennis has played 264 NRL games after breaking into first-grade with Newcastle in 2003.
The hooker has had stints with the Knights, Dragons, Broncos, Bulldogs and Sharks, and played eight games for NSW.
The 32-year old has an option on his contract to play another year, but said it was time to be a dad to his four kids.
“To have to say ‘no, no I can’t take you to the park. Dad’s got to stay at home and ice his leg’ or ‘dad can’t go there today, I’ve got training tomorrow’, It got to a certain point where I needed to make a decision around that,” he told radio station Triple M.