Former Labour finance minister Michael Cullen is leaving politics to take up the deputy chairmanship of New Zealand Post.

Dr Cullen held a media conference this afternoon to announce he had accepted the position at the state owned enterprise and would resign from Parliament at the end of the month.

He starts as a director on May 1 and becomes deputy chairman on October 1. Current chairman Jim Bolger is due to leave the role in October 2010 when it is likely that Dr Cullen will take over.

Kiwibank is a subsidiary of the NZ Post board and, though there is no guarantee that Dr Cullen will be on it, he is almost certain to have a role.

The former treaty negotiations minister said he would also act as principal advisor to the chair of Waikato-Tainui and expected to play a negotiating role with Ngati Tuwharetoa in their treaty negotiations.

"The time has come for me to move on so as to make sure the space is available for my colleagues in the Labour Party to move forward," Dr Cullen said.

"I have been privileged to serve in many different roles and hope that in my new ones I will be able to contribute positively to our nation's future."

As a list MP, Dr Cullen's departure will not prompt a by-election, first-in-line Damien O'Connor will take his seat.

State Owned Enterprises Minister Simon Power confirmed Dr Cullen's appointment to New Zealand Post in a statement today.

"I intend to offer 22 new appointments, one elevation of a deputy chair to chair, three elevations of a director to deputy chair, and 20 reappointments," he said.

"Hon Dr Michael Cullen has been appointed to the board of New Zealand Post, and is expected to become deputy chair in the medium term."

Other new appointments include new chairpersons David Clarke - at Kordia, Phil Lough - at Quotable Value and Sarah Astor at MetService.

More soon.