Dixon is heading to Japan on a two-year deal to play in the new Japanese League One competition, which begins in January 2022, though it is unclear which club he is joining.
Dixon (32) brought up his 100th game for the Highlanders in the Super Rugby Transtasman final against the Blues.
He began his Super Rugby career with the Hurricanes, before joining the Highlanders in 2015.
Dixon has co-captained the side with halfback Aaron Smith over the past few seasons and has been one of the team's most consistent performers, possessing one of the best lineout throws in the game.
Dixon said it was a difficult decision to leave.
“I’ve put a lot of thought into it and it was not an easy decision for myself and my family to make. I’ve had some incredibly great times with the team, and I will cherish them forever.”
Highlanders chief executive Roger Clark had high praise for Dixon, noting his "significant mana within the team".
Head coach Tony Brown said Dixon would leave a long-lasting legacy at the Highlanders.
“Ash will be remembered as one of the great Highlanders men; his contribution to the club both on and off the field has been immense.
"As co-captain he has been the ultimate professional and we wish him, Mikayla, Paiyton and Boston all the very best with this fantastic opportunity.”
New Zealand Rugby professional rugby and performance manager Chris Lendrum said Dixon occupied a unique place in the rugby whānau.
“Ash’s achievements speak to his character. He leaves as one of the most capped Māori All Blacks captains of all time, and a leader of huge influence for both the Highlanders and Hawke’s Bay.
“He is a Super Rugby champion and a Ranfurly Shield holder, but more importantly he personifies the values of Te Ara Rangatira, The Rugby Way."
