Ms. Ardern took control of the Labour Party in July after its leader, Andrew Little, quit amid dismal poll numbers. She enjoyed a wave of attention for her charisma, her youth (she is 37), and for condemning a television commentator’s question about whether employers have a right to know whether a woman plans to become a parent.
During the campaign, she emphasized issues including child poverty, environmental management and housing affordability.
In the end, however, her efforts appeared to have fallen short.
Neither of the main parties won a majority of the 120-seat Parliament, which means that National, with 58 seats, and Labour, with 45, will now try to court minor parties to form a coalition — a process that could take days or even weeks.
Given its advantage, National is more likely to succeed, but to do so, it will need support from Winston Peters, a populist whose right-leaning New Zealand First party won nine seats.
Mr. Peters, 72, who is poised to act as kingmaker, did not tip his hand on Saturday, boarding a ferry to go home as reporters peppered him with questions. He said he would reach a decision by Oct. 12.
(Although Mr. Peters leans to the right, he is unpredictable, and he could conceivably ally with Labour and the Green Party, which won 7 seats. Together, the three parties would have 61 votes, a knife-edge majority. That scenario is considered unlikely but not out of the realm of possibility.)
Amid blue balloons and triumphant applause, Mr. English, 55, told supporters at Sky City Casino in Auckland, “We gave it everything, and we got better and better.”
Ms. Ardern, despite the setback, remains a fresh face in New Zealand’s male-dominated politics, and she is expected to remain an electoral force. She helped revitalize Labour’s popularity and strongly improved the prospects for a party that in the 2014 election won just 25 percent of the vote.
Ms. Ardern reminded supporters that she had once called the Labour leader’s position “the worst job in politics,” adding that she had now changed her mind. She said that the party and its supporters had given it “their all” and that, while she had called Mr. English to acknowledge that National had won the most votes, she was not ready to…