The Wales international, who starred at the 2019 Rugby World Cup in Japan, was already in contract with the Blues and had the option of another year in the capital.
But he has now put pen to paper on a new deal that will take him through to 2024.
By then he would have had a 15-year spell at his home region.
Navidi, 29, said: “I’m delighted to sign a new four-year deal at Cardiff Blues. This is my home team, I have played all of my professional rugby here, and playing here has got me to where I am today.
“I am really grateful to have the opportunity continue my time here and I’m hugely excited about the future.
“With the squad we are building, with so much young talent breaking through each year to challenge the more established players, I am confident we can start challenging for honours again.
“We have had a good month and are now competing in both the Guinness PRO14 and Europe and I just want to do everything I can to ensure we have a good 2020 and continue to build.”
Navidi came through the Cardiff Blues academy system and made his senior debut in 2009. He has gone on to make 171 appearances for the region.
Now established on the international stage, the versatile back-row forward has won 23 Welsh caps. He played an integral role in the 2019 Six Nations Grand Slam and World Cup campaign.
He is the third back-rower to sign a new contract in recent weeks and Blues head coach John Mulvihill is pleased to secure another of his star performers.
Mulvihill said: “He was still in contract, but both Josh and the club were really keen to agree a new long-term deal and I’m delighted to have him here until 2024.
“He has consistently been one of Cardiff Blues’ best performers over the best part of a decade and he has now transferred that to the international stage which is fantastic.
“He is Cardiff Blues through and through and is really excited about the future here and he has a huge part to play in that.
“On the pitch he is an absolute warrior, whether with or without the ball. He is a fantastic bloke off the pitch and a brilliant role model for our younger players.”
