National MP Hamish Walker has announced that he will not be standing for re-election for the Southland electorate at the upcoming 2020 election.
The backbencher MP had been behind the leak of Covid-19 patient details to media.
"I wish to thank the people of Clutha-Southland who I have loved meeting, assisting and representing over the past two and a half years.
"I sincerely apologise for my actions," he said in a statement.
He said he would be making no further comment.
National Party leader Todd Muller said he had accepted Walker's decision to withdraw his candidacy for the seat of Southland.
"Rachel Bird, the National Party's southern regional chair, has received a letter from Hamish confirming he will withdraw as the National Party candidate for Southland.
"There was a clear breach of trust, which goes against the values National holds as a party.
"The National Party Board will still meet today to discuss the selection of a new candidate."
In another statement, party president Peter Goodfellow said the board met at midday today via videoconference and was advised that Walker had formally resigned his candidacy.
"A selection process will therefore begin almost immediately to find a new candidate for the Southland Electorate, and we look forward to a robust and democratic process.
"On behalf of the National Party board of directors, I would like to apologise for any distress caused to the individuals concerned as a result of the actions of one of our Members of Parliament."
It was revealed yesterday that former National Party president Michelle Boag was responsible for leaking Covid-19 patients details to Walker, who then passed that information on to media.
Prior to that revelation, Muller described the leak as "loose, shabby and a reminder these guys can't manage important things well".
Muller told Morning Report today there needed to be consequences and he has written to the party's board asking it to remove Walker from the party.
"This behaviour is completely unacceptable," Muller said.
Muller said he became aware that Walker was responsible for the leak on Monday and was awaiting legal advice before passing that information on.
He said he hasn't spoken to Boag about the issue and he's not sure what the arrangement between her and Walker is.
Boag this morning stood down as Auckland Central MP Nikki Kaye's campaign chair for the upcoming election and no longer has any role with the party. She has also resigned from her role as acting chief executive of the Auckland Rescue Helicopter Trust as a result of the leak, though she said she received the details via her personal email address.
"It doesn't support the values I bring to the role, and it doesn't support the values of the National Party I know," Muller said.
"I am personally, hugely angry. This is not the politics who reflects who I am as a person. It does not reflect the National Party."