Diskin, 31, is entering his fourth season with the Bulls, and has scored 12 tries in 69 appearances since joining from Leeds.
He said: “I am extremely proud to be continuing as captain.
“It is great to be the leader of a group of people who are very grounded and humble in how they go about their work.
“I am delighted to carry on in the role that has been bestowed on me, as we have some very talented young players coming through the ranks.
“Part of my responsibility is helping to guide them along the way and another part is leading the senior group, which me and the younger lads can tap into and breed a really good work ethic to bring back success to the club and to the city.”
Coach Francis Cummins has identified a leadership group within his squad, but has handed Diskin the captain’s armband for a third successive season.
“But Matt is the one that really stands out, as an overall captain.
“I am not guaranteeing he will play every week but he is the leader of this group and is a fantastic influence on the environment.”