The openside flanker, who has made 83 appearances since making his debut in 2011, was due to come out of contract in the summer and was attracting interest from rival clubs.
However, he has put pen to paper on a new deal at the Arms Park, following on from fellow academy products Lloyd Williams and Macauley Cook who signed last week.
Jenkins was pleased to commit his future to the Blues and is now focused on returning to action in the coming weeks.
He said: “I’m really happy to sign a new contract here. I’ve come through the Cardiff Blues system, it’s a region I’m very passionate about and I’m really optimistic about the future.
“It’s been great seeing so many of the other boys signing new deals and you only need to look at the likes of Dillon Lewis, Seb Davies and Owen Lane to see the talent coming through.
“I feel this is the best environment for me to continue improving and the competition for places in the back-row can only be beneficial to us all.
“I’m now looking forward to getting back on the pitch and contributing as much as I can in the second half of the season.”
Since making his debut six years ago, Jenkins has become an increasingly influential figure at the Arms Park.
The former Wales Under-20s captain has led the Blues on several occasions and was rewarded for his fine regional form with a place on Wales’ 2016 summer tour to New Zealand.
Cardiff Blues chief executive Richard Holland said: “It was always a main priority for us to retain the services of Ellis.
“He is a key figure and leader for us both on and off the pitch and will be instrumental in driving our rugby department going forward.
“He exudes all the qualities you would expect in a leader and is another example of a young, home grown player to have come through our pathway.
“It came as no surprise that there was rival interest in his signature but we are delighted he is staying at the Arms Park and are looking forward to seeing him back in action, and doing what he does best in the coming weeks.”