Speculation had been building for weeks that English, also a former Prime Minister, would step aside, and the decision became clear after the National Party met for a two-day conference in Tauranga last week, reports the Guardian.
"Now is the right time for me to step aside and embark on new professional and personal challenges. I informed the National caucus this morning that I am resigning as leader of the National party," English said at an emotional press conference on Tuesday morning, in which he teared up.
"I believe this will give National's new leader time to prepare the party for the 2020 election.
It has been a huge privilege to lead the party and serve in politics."
National Party secured 46 per cent of the vote in the September 2017 elections, giving it 58 seats in parliament, while Labour took home 35.8 per cent and 45 seats.
After weeks of deliberation kingmaker Winston Peters threw his support behind the Labour party, allowing them to form a coalition government with the Greens, with Jacinda Ardern as Prime Minister, the Guardian reported.
Ardern was one of the first to thank English for his public service after he announced his resignation.
"Just heard the news that Bill English has decided to stand down. Bill has made a huge contribution through his time in office and to politics generally. I admire those who serve NZ in this place, and Bill did for a long time...," the Prime Minister tweeted.
Nicknamed "Boring Bill English", he led the National Party to its worst ever defeat in 2002.
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