There was drama before kickoff when fullback Shaun Stevenson injured himself in the warm-up, meaning Caleb Makene switched to No 15 and Orbyn Leger moved onto the wing for his first start of the tournament. The Counties Manukau five-eighths acquitted himself well out of position.
At one point New Zealand had four first fives on the field, while Jordie Barrett even packed down on the side of a scrum, but it did not affect their flow.
Man of the match was Barrett, watched on by his parents in the stands, and his 15 point-haul and performance capped a special few hours for the Barrett family.
"We knew we had to play the full 80 to beat these guys. They stuck in there and play a similar style to us, so it was pretty had to combat them on defence," he said, adding that it was nice to get redemption after Australia had defeated them on the Gold Coast last month.
In the final, England overturned a disappointing Six Nations campaign to hammer Ireland 45-21, led by a 23-point haul, which included two tries, by captain and No 10 Harry Mallinder. This is England's third world Under 20 title, after championships in 2013 and 2014.
Argentina took third place, defeating South Africa 49-19, while Wales came seventh, dispatching Scotland 42-19. France edged Georgia 24-21 to place ninth, and Italy (41-17) consigned Japan to the 2017 World Rugby Trophy competition.
New Zealand 55 (Marino Mikaele-Tu'u, Hapakuki Moala-Liava'a, Quinten Strange, Isaia Walker-Leawere, Asafo Aumua, Peter Umaga-Jensen, Sio Tomkinson, Jonathan Taumateine tries; Jordie Barrett 6 con, pen) Australia 24 (Campbell Magnay, Fa'alele Sione tries, penalty try; Nick Jooste 2 con, James Tuttle con) HT: 21-21