“It’s been a privilege to be able to play for so long and captain such a great club,” Cayless said in a statement.
“I’ve had great support from my family, team-mates and people within the club. We’ve been through a lot of tough times and a lot of good times.
“Irrespective of what was happening this was always going to be my last year, I was always going to announce it once I’d finalised a couple of job positions.”
Cayless has vowed to help the Eels recover from their poor start to the season which has seen them fall to three defeats in their opening four matches.