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Mr Cull, in a brief written statement to the Otago Daily Times, confirmed he intended to stand down rather than seek re-election in October's local body elections.
At 69, Mr Cull who is also Local Government New Zealand president said he felt it was time to reduce his work demands and the commitments they required.
It would mark the end of his 12 years at the Dunedin City Council, the first three as a councillor and the last nine as mayor.
"I'll have a significant birthday next year and I want to step away while I am still fully enjoying the role and spend more quality time with my family.''
He thanked those, inside and outside the council, who had supported him in the role.
"I have learned and gained an enormous amount from many people and I am proud of what we have collectively achieved.
"I wish the incoming council and mayor all the best in building on those achievements.''
Mr Cull said tonight he would talk in more detail about his decision in the coming days.
The decision would also affect his role as LGNZ president, the rules for which limited eligibility to a sitting councillor or mayor. Mr Cull's decision would also likely throw the race to succeed him wide open.
So far, incumbent Green Party councillor Aaron Hawkins has confirmed his bid for the mayoralty, as have two candidates from outside council Scout Barbour-Evans and Carmen Houlahan.
Much anticipation will centre on three other potential contenders - incumbent councillors Lee Vandervis, Jim O'Malley and Christine Garey - who are all yet to publicly confirm whether they will seek the mayoralty.
Cr Conrad Stedman had also previously indicated he was considering a tilt, while Cr Andrew Whiley has said he remained "on the fence'' about a bid.
Attention will also turn to other potential candidates outside council, such as Barry Timmings, who stood unsuccessfully for mayor in 2016.