A previous version of this story incorrectly said McLean replaced Greg Miller as board chair. McLean's appointment as chair in early 2022 came soon after Miller quit as chief executive in late 2021. Reidy was previously chief executive at KiwiRail between 2014 and 2018.
The chair of KiwiRail's board, David McLean, has announced he will retire early from his position, effective 31 July.
Shareholding ministers Finance Minister Nicola Willis and State Owned Enterprises Minister Paul Goldsmith have accepted McLean's retirement, after he advised them of his intention on Wednesday.
"In my view, stepping aside from the start of the new financial year is best for the organisation as it enters a new phase of its development," McLean said in a statement on Sunday.
"I understand the government intends to announce my retirement today, so I have brought my announcement forward."
Willis said it was unrelated to the Aratere incident at the weekend.
McLean's term as chair was due to finish at the end of October. He joined the state-owned enterprise in 2021, coming from Westpac.
"I joined KiwiRail because I believe that rail has a critical role to play in New Zealand's future - transporting goods to market, reducing road congestion, and contributing to New Zealand's low carbon economy. I am proud of the role that KiwiRail plays and believe that it is in a strong position to build on this legacy.
"I leave with confidence in a team and an organisation that has dealt with many major challenges and is now in a much stronger and more stable position."
Current KiwiRail chief executive Peter Reidy was appointed under McLean's watch.
"I would like to acknowledge the rest of the KiwiRail noard, CEO Peter Reidy, and all of the people who work at KiwiRail," McLean said. "KiwiRail has a strong and passionate team, whose support and enthusiasm for the organisation will underpin the company's future success."
Prior to KiwiRail, McLean had held high-ranking positions at Victoria University of Wellington, Westpac and Kiwi Group Capital (Kiwibank, New Zealand Home Loan Company).
KiwiRail has recently been criticised by Transport Minister Simeon Brown, who last week said he was "highly unimpressed" with the state-owned enterprise's ferry maintenance programme.