The 36-year-old can now look forward to his 12th season in gold and blue after agreeing new terms.
And Gillies, who has also had playing spells at Richmond and Llanelli, revealed his delight at extending his stay.
"After such a long time at the club it's hard to imagine ever playing anywhere else," admitted Gillies. "Therefore it's massively pleasing to me to be offered a new deal and to agree terms to stay at Warriors.
"My ambition burns as strong as ever. If that ever goes out then you know the time is right to walk away, that does happen to people, but it's not the case with me.
"I still want to be first choice, but I've been around the game long enough to know that is now always possible.
"If not, I am there to support the other players and push the hard in training. It's about squads and a team effort these days; that is the mentality you have to adopt."
Head Coach Richard Hill has revealed his delight at the continued form and fitness of Gillies and the Glasgow-born forward admitted his rugby longevity was helped by the huge competition for places at Sixways.
"I'm pleased with the shape I am in and at 36-years-old I still feel I am contributing and feel I've got plenty left in the tank. I feel I am offering something every week - whether that is on the training field or in the games," said Gillies.
"I've had to take a back seat this season more than in previous years and mentally that can be hard to deal with. But, in terms of impact on the body, I feel that has helped my longevity and way I feel.
"It's hard to get used to not playing 80 minutes of every game like I have in previous seasons. But the other guys are playing exceptionally well so you understand the competition is fierce, all you can do is push your claims.
"We have got a very good group of locks at the club. Everyone is a different type of player and the coaches are able to mix and match as they see fit. Everyone has played their part this season.
"The club has become hugely important to me and my family," he added. "I still remember when I came to look around all those years ago and met John Brain and shortly after that Cecil Duckworth.
"Cecil always had a clear vision of where he wanted to take this club. A number of other top players that I have played with have also shared and bought into that vision.
"I want the club to be as successful as possible and I want to contribute as much as I can to that cause. We've always aimed to progress and push higher up the table - that is still the ultimate aim."