The versatile forward has established himself as an ever present figure since arriving at the Arms Park in 2014, making 157 appearances in all competitions.
He has played more minutes than any other Cardiff player in each of the last three seasons and has stepped in to lead the team on numerous occasions.
Turnbull now succeeds Ellis Jenkins on a permanent basis as Cardiff prepare to kick-off their United Rugby Championship season against Connacht on Friday night.
Director of Rugby, Dai Young said: “We’re really pleased to name Josh Turnbull as club captain ahead of the new season.
“Ellis Jenkins has done a great job over the past number of years, even when on the sidelines, and he remains a key player and leader for us.
“However, Josh stepped into that role on numerous occasions last season and I feel he deserves the opportunity to take that forward as club captain.
“He epitomises all of the qualities I want from a captain – he is very professional and diligent in his preparation, leads by example and gives his all in every training session and every minute on the pitch.
“He’s a very important player for us, who I am sure will do a brilliant job as captain but he will also be backed up by a group of other strong leaders within the group.”
Turnbull, 33, made 20 appearances last season and was rewarded for his rich vein of form with a call-up to Wayne Pivac’s Wales squad.
He currently stands third in the URC appearance charts and is relishing the opportunity to lead the Blue and Blacks back into action for a new season.
Turnbull said: “It’s a massive honour and privilege for both myself and my family to captain Cardiff and follow in the footsteps of so many great players.
“It’s always a proud moment to lead the boys out, particularly at the Arms Park, and it’s something I am really looking forward to doing once again as club captain.
“I am really excited about what this group can achieve, with Dai Young at the helm, the direction we are going and progress we are making.
“Hopefully I can play my part, lead by example and help drive standards but I will also be leaning on other boys in the squad who have captained the team like Ellis, Lloyd Williams, Kristian Dacey and Kirby Myhill.
“I am also very aware that I still need to perform to the very best of my ability on the pitch. We have a hugely competitive back five in the pack and I still have to earn my place on merit.”
