With all votes tallied, Ms Ardern's centre-left Labour Party won 49.1%, bringing a projected 64 seats and a rare outright parliamentary majority.
The opposition centre-right National Party won 26.8% in Saturday's poll - just 35 seats in the 120-seat assembly.
The poll was originally to be held in September but was postponed by a month after a renewed Covid-19 outbreak.
Ahead of Saturday's vote, more than a million people cast ballots in early polling, which opened on 3 October.
New Zealanders were also asked to vote in two referendums alongside the general election - the end of life choice on euthanasia and cannabis legalisation.