Having risen to attention at Swansea and gone to the 2003 World Cup as a youngster, Thomas was part of the inaugural Ospreys squad that year. He made his debut against Leinster that November, clocking up his 100th cap for the region five years later against Benetton Treviso in the Heineken Cup.
Speaking after signing his new deal, Thomas said: "I'm delighted to have re-signed. I've been an Osprey since we started back in 2003, I've gone through the inevitable highs and lows of the evolution of the place, and I suppose it's ingrained in me now as a person. I'm committed to carrying that on over the next few years and helping the Ospreys be as successful as possible.
"One of the main reasons for me committing to the Ospreys is that the people in charge here are quality people who are respected by everyone in the squad. When you are working with individuals of that calibre you just want to be a part of the environment they are creating, which is just getting better and better.
"We've had some good results and some success, but we've also had disappointments in Europe so there is so much we still want to achieve as a group and I believe that the environment being created here is one that can bring us continued success.
"Over the years I've probably become known as a utility player, and with hindsight it hasn't really helped me that much. One thing I'm really grateful for is Johnno's honesty, and he has given me some consistency with my play and that's all you can ask for really. I respect what he's done regarding my personal circumstances and position and I want to repay that."
Ospreys Director of Coaching, Scott Johnson, added: "Jonathan committing his future to the region is great news. He's still a young man but has great experience under his belt and he is a real influence in our environment. He's got such a positive attitude, he is constantly striving to improve himself and the team, and that is exactly what we want in the dressing room.
"As with Ryan who has also recently signed a new deal, he's a versatile athlete who understands that in the modern game it's not about second or back row. It's about being a back five player with the physicality, skills and intelligence to perform for the team regardless of the number on his back and it's fantastic for the region that he sees himself as a true Osprey."