Henson, who is a former Wales and British and Irish Lions player, will join up with the Men of Gwent this summer on a 2-year contract.
The double Grand-Slam winner, who currently plays for Bristol, recently put in a stunning Man of the Match performance against Bath, and his signing is a major coup for the Dragons.
After signing his contract, Henson commented: “I have really enjoyed my time here at Bristol but when the opportunity came along to join the Dragons and return to Wales, I couldn’t say no.
"I still have loads to offer and I know what Kingsley wants from me. I’m especially looking forward to pitting myself against the current Welsh players, and hopefully becoming a catalyst and mentor for the tremendous talent that is in the Dragons squad.”
Dragons Head Coach, Kingsley Jones added: “This is a hugely important signing and exactly what we need to complement our existing squad.
“I am delighted that Gavin sees the potential within the Region and that he is excited about the prospect of assisting this group of backs with their development.
“Having worked with Gavin previously I am fully aware that he will bring critical experience on the field and inside the training environment."
Dragons CEO Stuart Davies also commented: “It’s fantastic news for Dragons’ supporters and Welsh rugby in general that we are bringing back to Wales one of the finest players of a generation.
“I hope that securing the signature of one of the biggest names in the sport will give our supporters a timely lift and renewed hope for what next season might
The announcement regarding Henson follows hot on the heels of that of 30 cap Springbok, Zane Kirchner, and in