The England international joins the Bees with a wealth of experience, having won the Premier League and Champions League with Liverpool before leaving for Saudi club Al Ettifaq and then iconic Dutch side Ajax.
Henderson was contracted with the Eredivisie club until the summer of 2026 but took up an option to terminate his deal early and has now signed a two-year contract with Brentford.
"I'm delighted that I'm here; I'm very excited to get started and get going," the 35-year-old midfielder told Brentford's website.
"I've always had huge admiration for the club and what they've achieved over the last few years, in particular, how they've grown as a club.
"I've been told how organised and well-run the club is, it's very family-oriented, which I think is very important."
The 35-year-old joins in what is a summer of change for Brentford, who lost former manager Thomas Frank to Tottenham, captain Christian Norgaard to Arsenal and are facing the reported departures of top stars Bryan Mbeumo and Yoane Wissa.
Brentford manager Keith Andrews said: "When we became aware of Jordan's availability, it was a pretty simple decision.
"We did our due diligence around his recent games to see where he is. He's still phenomenally fit and he's still phenomenally motivated to achieve things in the game, having already achieved a lot.
"With the void of experienced players leaving the building - Christian Norgaard, Mark Flekken and Ben Mee - it was important to replace that.
"We've got a pretty young squad overall and we've got a lot of club experience, which is really important, with the likes of Vitaly Janelt, Mathias Jensen, Ethan Pinnock and Josh Dasilva, who is still at the club doing rehab.
"But what Jordan will bring is that he has been one of the most influential leaders in modern Premier League years. He's been at the forefront of driving for titles and Champions Leagues at a fantastic club.
"He also has experience at international level with England and, with that comes a level of experience, professionalism and dedication to his profession - that's the exact way we want to be as a football club.
"He will drive standards and be a brilliant addition to the squad."