Labour candidate Michael Wood has won the Mt Roskill seat and will be parliament's newest MP.
Mr Wood had a convincing lead over National's Parmjeet Parmar from the word go.
With 20 percent of the vote counted he lead by 2000 votes, that margin has increased to more than 6500.
With 100 percent of the vote counted Mr Wood had gained 11,170 against Ms Parmar's 4,652.
Roshan Nauhria of the NZ People's Party was running a distant third with 706.
A jubilant Michael Woods has addressed his supporters at his campaign party.
"It is a very good night to be Labour in Mt Roskill! And it is a very good night for everyone in this community who stood up and voted for this community to have a strong voice.
"It is a good night for everyone in this community who believes that every man woman and family should have decent affordable housing.
"It is a good night for everyone who believes that it has gone on for too long that we have traffic congestion in the city and that it is time to build first world public transport in Auckland," he said.
National candidate Parjeet Parmar has called Michael Wood to concede the by-election.
"It's disappointing but we knew getting into this by-election that it's hard for the government to win a seat from the opposition."
"Mt Roskill is a great place and I am very passionate about Mt Roskill families and businesses and this by election gave us the opportunity to be in front of people again, to talk about local issues that matter to our people."
Before the votes had even come in, a handful of complaints had - alleging breaches of electoral law.
The Electoral Commission has confirmed it has notified police about one of those complaints, regarding a protest held today.
Newshub understands it involved a group of Indian students outside Ms Parmar's electorate office.
The by-election will decided who replaces Phil Goff in parliament. He resigned the seat when he was elected mayor of Auckland in October. Mr Goff had held the seat since 1981, with a three-year break between 1990 and 1993.
Mr Goff mentored Mr Wood and says he is a deserving candidate.
"I'm very proud of the candidate that he has become. I think he will be a very good representative in this electorate."
"My pick is, if this election result is on merit Michael Wood will be the MP for Mt Roskill by 10 o'clock tonight."
He says despite an early lead, he does not want to be too confident about the result.
"I thought I knew how to pick election results and then Donald Trump got elected so I've given up that science."
There are 47,266 enrolled voters in the Auckland suburban electorate, 16,857 people voted.
Newshub / NZN