The Mt Albert by-election shows his party's campaign techniques are working, ahead of September's general election, Labour leader Andrew Little says.
Jacinda Ardern won the Auckland seat for Labour yesterday with more than 75 percent of the vote on a low turnout of just under 30 percent.
She was 8500 votes clear of her nearest rival, the Green Party's Julie Anne Genter.
Mr Little said even though National did not stand a candidate, Labour didn't take anything for granted and campaigned hard to keep the safe seat.
"I think if you look at you know, the combination of Mt Roskill by-election the local government election, and this election where we got our vote out because of the hard work that Jacinda and her team did. I feel very confident about the quality of our organisation and the issues that we've picked and what we're going to be campaigning on."
He said the party's coffers had not taken a big hit by having to fund a by-election campaign.
Meanwhile, the new MP for Mt Albert said the Labour Party will look to maintain the momentum of yesterday's win, in order to boost its party vote at the general election.
Ms Ardern, who up to now has been a list MP, told Wallace Chapman on Sunday Morning it was satisfying to win an electorate seat but the party vote remained crucial.
"It's always party votes that is the thing that determines who gets to make up government so that for every party, is going to be what we'll all be focussing on."
The Green Party's candidate, Julie Anne Genter, said she was not disappointed by her loss.
She said the by-election had shown Labour and the Greens can work constructively together, even if they were contesting the same seat.
Ms Genter said the margin of Ms Ardern's win was not a surprise.
"It's quite usual for the Green Party to get around this percentage in by-elections because usually we campaign for the party vote and many Green Party voters are used to giving their candidate vote to Labour."
The candidate for Gareth Morgan's Opportunities Party, Geoff Simmons, said he was happy with his showing.
Mr Simmons was well back in third place, with 600 - just under five percent.
He said the party achieved what it set out to do.
"We managed to get 5 percent within that time and lifted people's understanding of what the Opportunities Party is all about but there is a pretty big lot of apathy to overcome. Hopefully if we can tap into those people and motivate them to vote for something different then we'll have a chance in September."
Ms Ardern's win means Raymond Huo will re-enter Parliament as a list MP.