Labour says Poto Williams' anticipated victory in the Christchurch East by-election shows its message on helping the earthquake-ravaged city is getting through.
Ms Williams secured 8119 votes, more than 60 percent of votes cast, to take the seat vacated by Labour's Lianne Dalziel when she successfully contested the Christchurch mayoralty.
Ms Williams won by 4613 votes from the runner-up, National's Matthew Doocey.
Labour leader David Cunliffe says Ms Williams will make an excellent MP.
He says the party's campaign in Christchurch East was run and won on the issues facing the city.
"On housing, insurance and standing up for people in the rebuild, voters heard and embraced Labour's vision," he said.
"We will continue to campaign on these issues for all of Christchurch all the way through to the next election."
Ms Williams said she was humbled by the result and would do all she could to advocate for the people of the electorate.
Mr Doocey said he took the highly visible presence of Mr Cunliffe in the campaign as a sign that he was a credible opponent.
"At times I wasn't sure if I was standing against Poto Williams or David himself," he said.
The Green Party's David Moorhouse was a distant third with 926 votes, but he said the party did well to increase its electorate vote from 4.7 per cent to 7 per cent.
Just 13,318 people voted in the by-election, an estimated 41.4 per cent of registered voters and well down on the 28,977 people who voted in the electorate in the 2011 general election.
An estimated 590 special votes have to be counted before the result is finalised.