''To all the staunch supporters who have supported myself and the Magpies through thick and thin, you are not forgotten, thank you.''
Dixon will play in the new Japanese League One competition for NEC Green Rockets.
The Magpies captain and Highlanders co-captain has been one of NZ provincial rugby's most consistent performers in recent seasons.
Dixon played his 100th game for the Magpies in last year's memorable Ranfurly Shield victory over Otago, and this Saturday's Shield defence, also against Otago, in Napier will be his 110th match.
Hawke's Bay Rugby CEO Jay Campbell said Dixon had arrived in the Bay as a highly promising hooker out of Christchurch Boys' High.
''[He] won the hearts and minds of fans throughout the country for the way he conducts himself on and off the field and always giving 100 per cent every time he represented Napier Tech, Magpies, Highlanders and the Māori All Blacks.
"Ash departs as one of the greats to represent our province."
Magpies head coach Mark Ozich said the Japanese experience would be a great one for ''a real warrior of New Zealand rugby".
"Whilst losing someone of Ash's ability, stature and leadership is a huge loss, I can understand the timing is right for him.''
New Zealand Rugby general manager professional rugby and performance Chris Lendrum said Dixon occupied a unique place in NZ's 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.''