New Zealand’s Prime Minister Jacinda Ardern will take her time to decide whether she will go alone or include coalition partners in her next government, after a thumping election win on Saturday.

Ardern delivered the biggest election victory for her centre-left Labour Party in half a century, which allows her to govern alone. It is the first time any party has had enough support to be a single-party government since New Zealand adopted a proportional voting system in 1996...