It is not known if the strength of internal party support for the new Labour leader in Britain will translate to the polls.
Radical left-wing politician Jeremy Corbyn won with 59.5 percent of votes cast by the party's members and supporters.
Prime Minister John Key says it will be interesting to see if the public give him the same level of backing because most voters usually "live in the middle".
"That's the problem when you have your party select the leader because your activists are by definition really tuned in and they could be incredibly left-wing," he told the Paul Henry programme.
"The National Party core support base is probably a bit more right-wing than the Government is, so if they were to selecting the leader they might select a leader different from me, but the question is could you carry the public?"
Mr Corbyn has begun the task of appointing a new shadow cabinet.
Eight senior Labour MPs have already quit the front bench as they don't want to work with him.