The former England second-row, who turns 35 next month, has signed a fresh one-year contract for 2017 after discovering some of his best form this term.
He has been one of the stand-out performers for fourth-placed Hull so far having battled back from the serious injury that wrecked his last campaign.
“It was one of my goals at the start of the year, knowing that my contract would be up, to secure a new deal, especially with the injury I suffered last season,” said the former Leeds Rhinos forward, who initially joined in 2013 after a fine career with NRL club Wests Tigers.
“Before I got it signed it was obviously up in the air but I was determined as I’ve been enjoying playing and I still want to achieve things at this club.
“To get it done is a relief and a massive motivation to do well. It has worked out well and it’s nice to get it put to bed so we can crack on.”
Ellis has missed the last two games with a rib injury but hopes to return to action at Wakefield - where he started his career - on Sunday.
Hull coach Lee Radford admitted: “I’m really pleased for Gaz.
“It’s fantastic that he is staying and wants to go around again.
“Our recruitment for 2017 won’t be as busy as it has been; we are looking for continuity and Gaz is a central part of that.
“We believe we have a good squad, a competitive squad and maintaining that moving forward is key, built around people like him.
“He has shown in the games he has played how important he is for us.
“His actions and leadership will be key over the coming seasons in our quest for success.
“As well as his efforts on the field he is a role model off it for any budding young player.
“He leads by example in how he goes about his business and his influence on the squad and the relationship between coach and captain is an integral part of any organisation.
“Gaz has a leadership role and influence that will be invaluable for our group of young, English forwards like Chris Green, Jordan Thompson, Josh Bowden, Scott Taylor, Liam Watts and Jansin Turgut.”