He has endorsed a call by the Green Party to modernise the oath through a cross-party forum - a move that is also supported by Labour's Mr Shearer.
"My personal feeling is that I'd rather swear an oath to all New Zealanders, rather than the Queen," Mr Shearer said. Asked if he would include the Queen in a personal oath, he said: "Not necessarily."
However, Mr Key did not support changing the oath.
"The Queen is New Zealand's head of state. That's the constitutional monarchy system that we have and I think every MP therefore is bound by that and should swear their allegiance to the Queen."
Mr Shearer, who supports New Zealand becoming a republic, said Mr Key should at least be open to a discussion.
"Mr Key talks about moving eventually to a republic and that we will inevitably go there ... If we're inevitably going to go there, what's wrong with taking a look at the oath to start with?"
In a Green Party-run online survey with more than 650 responses, 75 per cent opposed the current oath to the Queen.
More than 90 per cent would support an alternative oath in which MPs pledged to do their best for New Zealand.
Green Party co-leader Metiria Turei called for a cross-party process to modernise the oath.
"We do not serve as MPs out of any sense of loyalty to the British monarch - our loyalty is to New Zealand and our unique place in the world."
Labour yesterday endorsed Lockwood Smith's re-election as Speaker of the House, in contrast to the beginning of the previous parliamentary term, when the party voiced some concerns.
Oath more popular
Two thirds of the MPs gave the oath at the swearing in to Parliament yesterday, rather than the more secular affirmation.
The oath ends with "so help me God" and is usually given over a Bible. Labour MP Raymond Huo used his own Holy Book of Buddhism, the Diamond Sutra.
National MPs were far more likely to choose the oath than other parties - of the 59, only six gave the affirmation instead: Amy Adams, Kanwaljit Singh Bakshi, Maggie Barry, Jami-Lee Ross, Maurice Williamson and Jian Yang. Labour was fairly evenly split - 17 gave the oath while 14 gave the affirmation. Three MPs were absent (Maryan Street, Charles Chauvel and Annette King).
Five NZ First MPs delivered the oath, including leader Winston Peters, and three took the affirmation. All 14 Green MPs gave the affirmation - four of them in te reo Maori. Of the 10 party leaders, seven swore the oath: Prime Minister John Key, Labour leader David Shearer, Maori Party co-leaders Pita Sharples and Tariana Turia, NZ First leader Winston Peters, Act's John Banks and United Future's Peter Dunne. The Green Party co-leaders Russel Norman and Metiria Turei chose the affirmation as did
Mana Party leader Hone Harawira.
THE OATH
I, ... , swear that I will be faithful and bear true allegiance to Her Majesty Queen Elizabeth the Second, her heirs and successors, according to law. So help me God.