Man-of-the-match Styris's 91-ball 87 was the centrepiece of New Zealand's 266 for five, which also featured a rapid fifty from his fellow all-rounder Jacob Oram.
England in reply were bowled out for 215 as Kevin Pietersen's first match as captain ended in defeat and a 3-1 series win for New Zealand.
Opposing skipper Daniel Vettori took three wickets for 32 runs in his 10 overs of left-arm spin after teenage quick Tim Southee (three for 49), the man of the series in his maiden ODI campaign with 13 wickets in all, had again claimed key scalps at the top of the order.
Owais Shah's 69 off 75 balls on his Middlesex home ground was the only significant innings of note as England's batting let them down again.
"We have a group of guys who have played less than 10 one-day internationals and when you get performances out of those guys you get pretty excited," Vettori said afterwards. "We have a team who can take us to the next level."
Styris added: "We knew if we could preserve wickets we'd have a chance."
Meanwhile an elated Southee said of his award: "It's an awesome achievement and something I'll remember forever."
New Zealand, well-beaten 2-0 by England in the preceding Test series and thrashed by nine wickets in the lone Twenty20 international were hammered by 114 runs in the opening match of this NatWest Series at the Riverside.
They then suffered the frustration of a no-result washout at Edgbaston with the game an over away from being declared a match.
Despite being bowled out for 182 at Bristol, they won the third one-dayer by 22 runs before holding their nerve to clinch a one-wicket win off the last ball at The Oval on Wednesday.
"The guys showed a lot of character. We have found it hard on this tour but we are a confident one-day team," said Oram.
Pietersen, leading England for the first time after regular one-day captain Paul Collingwood was banned for four matches following the team's slow over-rate at The Oval, said the team's batting was not up to standard.
"We didn't bat well enough this series, the consistency wasn't there. It's something we need to work on."
New Zealand made a slow start at Lord's after losing the toss but added 96 runs in the final 10 overs, 61 in the last five alone.
All-rounders Styris and Grant Elliott (23 not out) put on an unbroken 65 for the sixth wicket.
The 32-year-old Styris, appearing in his 152nd one-day international, struck three sixes and five fours.
Together with the big-hitting Oram he upped the tempo with a run-a-ball fifth wicket stand of 77.
England openers Ian Bell and Alastair Cook shared a fifty stand only for both to depart in quick succession as their side slumped to 60 for two.
Bell, aiming across the line, was plumb lbw for a 27 featuring five fours. Then left-hander Cook, recalled for his first ODI since February, was caught behind off the 19-year-old Southee's second ball for 24.
Star batsman Pietersen ell for just six when his fierce square cut off Southee was well-caught by Oram at point.
And it wasn't long before 86 for three became 101 for four when Ravi Bopara was deceived by Vettori and bowled for 30.
Vettori also dismissed Luke Wright and Tim Ambrose for just eight runs between them and when Graeme Swann fell to a brilliant diving catch by wicket-keeper McCullum, England were 164 for seven and long out of the game.
Shah holed out off a Southee full toss before Mark Gillespie ended the match by dismissing James Anderson.
Styris, dropped on 13 off a difficult chance, also survived a tight stumping call on 39.
He was content to play second fiddle while Oram struck 52 off 40 balls, including three sixes and two fours.
The tall left-hander eventually holed out to off-spinner Swann who finished with an impressive haul of two for 33 in 10 overs.