The board will appoint two people to take over his role, one to head its investment arm and the other its distribution arm.
Known to his friends simply as T, the kaumatua expressed great satisfaction with his achievements in the past 14 years and said now was a good time to be leaving.
"It's a good time, with the arbitration and also the Treaty settlement," Tibble said, referring to the iwi's success in a long-running dispute over the value of the 20ha of ex-railway land around Auckland's waterfront and Treaty of Waitangi settlement.
"We put a lot of work into it," he said of the railway land deal, crediting the strong team led by barrister Liam McEntegart.
Horsley said the outcome showed Tibble's abilities.
"He picks the best consultants in their field and Liam is an example of that.
"The board also had engineer Peter Millar, who has been outstanding, and they also pulled in Peter Snelling, who used to head Tramco, as an adviser."
Tibble said it was time to move on and described as amazing his farewell at the marae this month, where he was presented with a whalebone patu.
Horsley, in Europe at the time, said he spoke to the gathering via Skype.
Before the chief executive role, Tibble was the company secretary and financial controller at the Maori Development Corporation and he took over at Ngati Whatua in 1998. He remains a Radio New Zealand director.
As head of the Auckland-based board, Tibble has been one of the most successful bosses of any iwi.
The board had around $30 million equity when he was appointed but the accounts for the year to June 30, 2011 showed assets of $518 million, including the proposed WAI 388 Treaty of Waitangi settlement.
But some of his achievements have left others smarting, particularly owners of more than 300 apartments on board land and others fighting over the navy land at Fort Takapuna on the North Shore.
The Herald has discovered that this month retired High Court judge Robert Fisher, QC, ruled the board had achieved a $12.3 million valuation on its 7054sq m Terraces apartment site in Parnell, where experts for the lessees had sought a $6 million to $7 million valuation. "We're not going to disclose the outcome of that claim," Tibble said, adding that the arbitration decision on the value of the BNZ and GE Money office blocks at Quay Park had also been issued and nor would he reveal that, except to say he was satisfied with the outcome.
Tibble drove WAI 388, the claim covering the loss of 32,000ha in the Tamaki isthmus, parts of the North Shore and West Auckland, the seabed, foreshore and reclamations in the Waitemata Harbour and northern parts of the Manukau Harbour.
He said he took satisfaction in the progress of the claim.
KEY ASSETS
* $250m: Rail land properties.
* $120m: North Shore ex-navy land.
* $84m: Eastcliffe Retirement Village.
* $34m: Other leasehold properties.
* $28m: Social and cultural assets.
* $2m: Joint venture interest in former Tamaki College land.
[Source: Ngati Whatua 2011 annual report]