Bill English says his active Catholicism has shaped his morals, but will not define him as Prime Minister.
Mr English and Paula Bennett have been formally voted in as the new leader and deputy leader of the National Party at a caucus meeting this morning.
Outgoing Prime Minister John Key announced a week ago he was standing down, saying he could not commit to a full fourth parliamentary term.
Both Mr English and Ms Bennett were elected unopposed by their caucus colleagues, after senior ministers Jonathan Coleman and Judith Collins withdrew from the leadership contest last week.
Transport Minister Simon Bridges withdrew from the deputy leadership race on Saturday.
Mr English, finally allowing himself to smile after a week of waiting to be confirmed as Mr Key's replacement, said he was "excited ... to be leading a strong team of MPs, full of ideas".
He was proud to announce Mrs Bennett - a "smart, accomplished and energetic woman" as his deputy, he said.
"She brings with her the political experience of winning and holding marginal seats ... and an inspiring journey from teenage solo mum to deputy prime minister of New Zealand."
Just minutes into a press conference to announce the leadership result, Mr English was asked whether his religious views would shape how he governed.
He has previously voted against, or said he opposes, marriage equality, abortion and euthanasia.
He was still an "active Catholic", he said - joking that it was "no guarantee of virtue or perfection".
"It's been an influence in forming my judgement, forming my conscience ... I recognise that other people have different sets of beliefs ... It doesn't define me."
He also backtracked on his previous opposition to marriage equality, saying he would probably now vote differently.
"Just seeing the impact it's had for couples, and the fact that it doesn't hurt marriage. In some ways it's an affirmation of the concept."
Mrs Bennett said it was an honour and privilege to be selected as deputy leader.
She said the past couple of days had been a chance to reflect on where she had been as a teenage parent and where she was now.
"There was a moment when I was a 17-year-old Māori solo mum in Taupō ... and I didn't have a job and it looked pretty bleak, actually."
It was a credit to New Zealand that she had been given a second chance, and the same chance was there for other teenage parents, she said.
"They'll be sitting there going, 'All right for her to say,' and it's really hard to see beyond the day, let alone to see where you could be in a week, a month, a year from now.
"I ... recognise that what I'm asking of them is a really big call."
Mr English said he would announce a new Cabinet line-up before Christmas.
He has already said he would hand his Finance Minister role to senior minister Steven Joyce, but would not give anything away about other changes.
He was unlikely to take on a particular portfolio himself, he said.
No pledge on superannuation
Mr Key, as Prime Minister, promised to resign if the government raised the age of eligibility for superannuation.
However, Mr English said he was not making the same pledge.
"That was a product of its time, when there was a need to establish trust, and I think it was a sound decision then," he said.
"I think now we have built credibility as a government that we will support those who are dependent on government for income, we won't put them in a worse position, we'll work to get them in a better position and that ... Is currently the policy."
Mr English would also not be drawn on whether he would call an early election to avoid a by-election in the Mt Albert electorate, which Labour MP David Shearer is vacating.
"We're driven by what works for New Zealand, not what works for the Labour Party."
Mr Key and Mr English will head to Government House early this afternoon, where Mr Key will formally tender his resignation and Mr English will be sworn in as New Zealand's 39th Prime Minister.
National MPs united heading to vote
Earlier, National MPs presented a united front heading into the caucus meeting, saying they were excited about the incoming leadership.
In response to a comment that he looked "deflated", backbencher Mark Mitchell said, "Hopefully I don't."
"I'm excited and energised."
That comment was echoed by senior minister Steven Joyce.
Mr Joyce said he would be "a typical finance minister, with some interests in particular areas".
The only politician not completely holding to the party line was Attorney-General Chris Finlayson, who expressed reservations about the Cabinet shake-up that backbenchers reportedly want.
"Some of them need to learn to walk before they run," Mr Finlayson said.