Gatland, 28, will play for Kobelco Kobe Steelers alongside Chiefs teammate Brodie Retallick.
Gatland's season in DHL Super Rugby Pacific was cut short when he suffered a distal bicep tendon rupture in round 11 against the Highlanders.
Gatland, who first played Super Rugby for the Blues and Highlanders, joined the Chiefs in 2020, having played in the National Provincial Championship for Waikato before his transfer to North Harbour.
Gatland played 54 games for North Harbour, scoring 600 points. He made 15 appearances for the Blues and scored 60 points and eight games for the Highlanders. He played 32 times for the Chiefs and scored 176 points.
He said, "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."
Chiefs coach Clayton McMillan said Gatland had contributed to the Chiefs in his three years with the side.
"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.
"I am gutted for Bryn that injury prematurely ended his season and the potential for higher honours because he deserved it."