He's has signed a deal with Kobe Steelers.
Gatland will link up with his Chiefs teammate, All Blacks lock Brodie Retallick, at Kobe, with the latter announcing his departure earlier this year.
Chiefs head coach Clayton McMillan praised Gatland's character and abilities.
"Bryn has been an excellent Chief over the last three years. He is an experienced and calm tactician, an outstanding goal kicker and a tough defender. These qualities will serve him well as he embarks on the next phase of his rugby journey."
Gatland has had a strong Super Rugby Pacific season which was cut short after he suffered a bicep tendon rupture in round 11 against the Highlanders.
"I am gutted for Bryn that injury prematurely ended his season and the potential for higher honours because he deserved it. We wish him well with his recovery and the opportunity in Japan," said McMillan.
Gatland grew up in the Chiefs region and kicked off his rugby career at Hamilton Boys High School. He soon joined Waikato for the NPC championship, before he made the shift to represent North Harbour.
Boasting over 50 Super Rugby caps, Gatland played for the Blues and Highlanders, before joining the Gallagher Chiefs in 2020 where he notched up most of his starts.
Gatland said it will be tough to leave the Chiefs behind, but he believes he's made the right choice.
"Goodbyes are never easy, but it's time for me to move on to a new challenge and experience in my career.
"I've loved my time at the Chiefs and want to thank everyone involved in helping fulfil the dream of a 10-year-old kid born and raised here. This team will always hold a special place in my heart and I will always continue to support from wherever I am."
This week the Chiefs host the Brumbies in Hamilton in the Super Rugby semi-finals, with the winner to play either the Blues or the Crusaders for the title.