National's education spokeswoman Katherine Rich has announced she will stand down from politics at the election to spend more time with her young children.
The loss of one of National's most high profile women MPs is a blow to the party, but leader John Key quickly announced her
education portfolio would be taken over by East Coast MP Anne Tolley.
As a result of the changes Mrs Tolley will move to number 10 in the party's ranking.
Mrs Rich, 40, first entered Parliament on National's list in 1999.
"Being a minister in John Key's cabinet would have been a huge privilege and honour for me," she said.
"I do not doubt my ability to fill such a role. However, after much thought, I have reluctantly come to the conclusion that with two young children I would not have been able to do justice to it without unfairly impacting on their lives," she said.
"Over the summer I had a chance to think about the future for my children and my family and concluded that it's time to move on to face new challenges."
Mrs Rich, who is National's education spokeswoman, has two young children and her husband Andrew has two other children from a previous relationship.
She said she would continue as an MP and in her select committee roles up until the election.
Mr Key said he greatly regretted losing Mrs Rich, but understood her reasons.
But he had confidence in Mrs Tolley to step up and take over the education portfolio.
"I have a great deal of confidence in Anne's abilities. She has proven herself since the time she re-entered Parliament in 2005."
Mrs Tolley, who also did a stint as a list MP between 1999 and 2002, had relinquished her chief whip role, which would be taken on by first term list MP Nathan Guy.
Napier MP Chris Tremain would take over the junior whip role formerly held by Mr Guy.
Mr Key said associate education spokesman Allan Peachey would now become "deputy" education spokesman.
- NZPA
