Prime Minister John Key says senior Minister Simon Power has handed over the State Owned Enterprises portfolio to Tony Ryall.
"Mr Power approached me yesterday indicating that because of his impending retirement from Parliament, this change should be made," Key said.
Key said the change was being made because of Power's concern that if he remained in the portfolio there could be a perception of a conflict of interest as he made the transition to the commercial world after the election.
Simon Power announced last month that he was retiring from politics, despite being widely tipped as a future prime minister.
The fourth-ranked minister in Key's National-led government will finish up after the election.
Announcing his retirement in March, Power said that he was privileged to have served in cabinet and as the Member for Rangitikei since 1999 but "I feel it's time to move on to something else".
Power is Minister of Justice, Minister of Commerce, Minister for State Owned Enterprises, Minister responsible for the Law Commission, Associate Minister of Finance, and Deputy Leader of the House.
At the time he said the would stay in his portfolios until the election but appears to have changed his mind. Power will return to work in the private sector.
Key thanked Power today for his efforts in the SOE role.
"I want to place on record my thanks for Mr Power's work in the SOEs portfolio where he has made a big contribution, including work on the development of the Government's proposed mixed ownership model."
The change in portfolios takes effect immediately.