National did not contest the byelection, and with preliminary votes counted Ardern had 10,000 votes (77 per cent).
The Green Party's Julie Anne Genter was second with 1489 votes (11 per cent).
Ardern was joined by Labour leader Andrew Little and other senior MPs including Phil Twyford at the Pt Chevalier Bowling Club last night. There had been speculation that a strong byelection showing could lead to some within Labour questioning whether Ardern should be elevated to the deputy leader position, currently held by Annette King.
"There is no vacancy," Little said when asked about that speculation. "I'm not planning on any changes."
Preliminary turnout was very low - at 29.9 per cent of the 45,200 enrolled voters in Mt Albert.
That compared to Mt Roskill where turnout was 38.5 per cent and 65 per cent for the Northland byelection last year.
Turnout plummeted to 32.8 per cent for Te Tai Hauauru in 2004, when Tariana Turia resigned from Labour to contest the seat for the Maori Party. Neither Labour nor National fielded a candidate.
Speaking to the crowd, Ardern paid tribute to former MP David Shearer, and also previous Mt Albert MP and Prime Minister Helen Clark.
"Here in Mt Albert there is so much to celebrate but we need to go back to the basics - affordable houses, the ability to get around our city.
"I vow that I will advocate for all these things. But real change comes when Labour are in Government. Tonight is the first step, and now the real work begins."
Ardern paid tribute to Genter, saying they had set out to model a healthy contest and she believed that had happened.
Little said the strong result showed Labour was in fine shape to fight September's general election.
"It's all on for September ... we are on our way."
Shearer won Mt Albert in the 2014 general election with about 59 per cent of the total. In the 2009 byelection that saw him enter Parliament, Shearer got 13,260 votes - about 63 per cent of the vote.
Thirteen candidates competed for Shearer's seat after the former Labour MP and party leader resigned in December to take up a United Nations posting in South Sudan.
New Zealand's newest party, The Opportunities Party headed by Gareth Morgan, stood in the byelection. Its candidate, ex-Morgan Foundation staffer Geoff Simmons, had 4 per cent of the vote.
Ardern is a list MP and her victory will mean another Labour list MP will come into Parliament. That will be former MP Raymond Huo.
Genter, who is highly rated within the party and is its transport, health and Auckland issues spokeswoman, will be disappointed with her result.
In 2014 more than 8000 people in Mt Albert gave their party vote to the Greens (just over 20 per cent), and then candidate David Clendon got 3000 votes, or 9 per cent.
Ardern recently moved into Mt Albert with her partner Clarke Gayford but had been intending to stand in Auckland Central for the third time prior to Shearer's resignation.
National's decision not to stand in Mt Albert came after its candidate Parmjeet Parmar lost heavily to Labour's Michael Wood in the Mt Roskill byelection in December.
The Green Party did not stand in that byelection, a decision reached after Labour and the Greens signed a Memorandum of Understanding, with the aim of changing the Government.
