Drawing a line under nine years of conservative rule, the country voted decisively for change yesterday, ousting Jenny Shipley's National Party government and giving Labour the largest number of seats in the parliament in Wellington.
Coalition talks will begin in Auckland today, but there seems little doubt that Ms Clark - almost dumped by her own party three years ago - will lead New Zealand into the new millennium at the head of a centre- left government.
Addressing a euphoric crowd of party workers and supporters at Avondale Racecourse, in her Mount Albert constituency in west Auckland, she said: "For me, this campaign has been about articulating basic New Zealand values of fairness and opportunity and security. It has been about a vision for a better society."
Gracious in defeat, Mrs Shipley conceded at 11.30pm, telephoning Ms Clark to offer her congratulations. Shortly afterwards, she told a National Party gathering in the town of Ashburton, in her South Island electorate: "New Zealanders have decided that it is not our turn."
With the count almost completed, Labour had 38.9 per cent of the vote and its left-wing ally, the Alliance, 7.9 per cent, giving them a six- seat majority in the 120-seat, single-chamber parliament. National was on 30.7 per cent.
Although expected, it was an exciting conclusion to the first contest in a Western democracy between two female party leaders. Ms Clark, a former political science lecturer, can claim the distinction of being New Zealand's first elected woman prime minister; Mrs Shipley, 47, came to office after mounting a coup against her predecessor, Jim Bolger, two years ago.
A poised and cool personality, Ms Clark, 49, is widely admired for her intellectual skills but lacks Mrs Shipley's populist appeal. A lover of opera and cross-country skiing, she is said by critics to be out of touch with the lives of ordinary New Zealanders.
In Avondale last night, though, the party faithful could not get enough of her. Chanting "Helen, Helen," they showered her with red rose petals and fought for the chance to shake her hand. One supporter, standing on a chair for a better view, was knocked over in the crush.
Ms Clark's most committed fan was a heavily pregnant woman whose contractions began as the early results filtered in. "They're coming every 20 minutes," she said. "I just want to see Helen, then I'll get down the hospital."
The night brought some dramatic upsets. Winston Peters, the maverick Maori politician whose party, New Zealand First, held the balance of power after the last election, lost the Tauranga seat that he had represented for 15 years. The right-wing ACT New Zealand party, which campaigned for restrictions on Maori land claims, polled just 7 per cent, significantly less than anticipated.
The Green Party, which had been expected to send MPs to Wellington for the first time, fell just short of the 4.9 per cent required to give it seats under the country's system of proportional representation. It also failed, after a knife-edge contest, to take the key constituency of Coromandel from National.
Eighteen Maori MPs were elected, the highest number this century. One of parliament's more unusual new members will be Georgina Beyer, a former stripper and male prostitute who was George Bertrand until she had a sex change operation. She is now a Labour MP.
Ms Clark campaigned on a moderate platform, promising more money for health and education and a tax rise for high earners. A politician of pragmatism rather than bold ideas, she models herself on Scandinavian social democrats such as Gro Harlem Brundtland, the former Norwegian prime minister.
Government will not be an easy ride, thanks to the PR system, which makes it virtually impossible for one party to secure an overall majority. Although the Alliance is committed to working with Labour, there are significant policy differences be- tween the two parties and personal relations between Ms Clark and Jim Anderton, the Alliance leader, are frosty.
Mr Anderton, who would be deputy prime minister in a coalition government, quit the Labour Party in 1989, disgusted by the free market reforms that it had instituted in government.
Last night Ms Clark was conciliatory, declaring that "the level of working relations we have had with Jim Anderton and his party has made tonight's result possible". She said that she expected coalition talks to be completed by Christmas.
A difficult few weeks lie ahead. But Ms Clark, a keen hiker who climbed Mount Kilimanjaro earlier this year, has already scaled her most challenging political peak.