Former Prime Minister Bill English has quit as leader of the National Party, bringing his 14-month stint at the party's helm to a close.

Mr English, who has been an MP for 28 years, also quit Parliament.

He twice led the National Party to defeat in an election, and announced he was stepping aside to give his party a chance to regroup from its dramatic fall from parliamentary grace.

On election night, National-ACT held a three-seat edge over their Labour-Greens rivals, but still fell four seats short of a clear majority.

Over the next 26 days, both parties courted the nine seats offered by NZ First, until Winston Peters eventually sided with Labour and the Greens to overturn the three-term National government and end Mr English's short 10-month stint as New Zealand's 39th Prime Minister.

"We will be by far the strongest opposition party this Parliament has seen because nearly one in two New Zealanders supported us," he said afterwards.

"And for a party going into opposition, we're in the best shape you've ever seen - there's talent, energy, a group of people who were geared up to be the government."

While gracious in defeat, Mr English signalled his own future as leader would be up for discussion in coming weeks.

Through his eight years as Deputy Prime Minister, Mr English fashioned a formidable combination with Sir John Key and loomed as the logical successor when his boss resigned last December.

Less than five months ago, he seemed a hot favourite to retain the Prime Minister role, with National polling 20 points clear of Labour.

Significantly, though, a Labour-Greens-NZ First coalition would still have held sway - and after newcomer Jacinda Ardern was promoted to Labour leader on August 1, she swung and maintained just enough momentum to snatch power.

Newshub.

