Tries in each half from Munster captain Heather O'Brien and Alison Miller saw the girls in green achieve a memorable win over the four-time World Cup winners in Marcoussis, France.
The Black Ferns, led 8-7 at half-time off the back of a Selica Winiata try against the run of play.
Kelly Brazier's second penalty of the evening extended their advantage to 11-7, but Philip Doyle's charges defended doggedly in a tight third quarter and full-back Briggs countered brilliantly to create Miller's lung-busting score on the hour mark.
Briggs followed up with a stunning conversion from the touchline and although Brazier managed to bring New Zealand level at 14-all, a final penalty from the Dungarvan woman with 10 minutes left was enough to seal a stunning victory.
Their second successive triumph in Pool B means Ireland are on course to reach the semi-finals for the first time. They will aim to book that place in the last-four when they play Kazakhstan on Saturday afternoon.
Fiona Coghlan and her team-mates were relishing this rare opportunity to test themselves against the world's top-ranked team, and hoping to do what no Ireland 15s side (male or female) had done before - beat New Zealand at international level.
The girls in green drew plenty of confidence from the dominance they exerted during the first 20 minutes against New Zealand, although full-back Briggs missed a sixth minute chance to open the scoring from the kicking tee.
Their best passage of play saw flanker Paula Fitzpatrick - the only change from last Friday's win over the USA - barrel into the 22 and the Irish forwards took up the baton collectively.
They wheeled a New Zealand scrum into turnover ball and from their own set piece, the match officials missed blindside Rawinia Everitt breaking early to prevent a certain Irish try just a metre from the line. There was no penalty try awarded and the Kiwis were let off the hook.
O'Brien was bundled into touch at the subsequent scrum and New Zealand managed to hit the front in the 22nd minute. Their Sevens captain Huriana Manuel made ground in midfield and Claire Molloy was pinged at the ruck, with out-half Brazier taking the three points on offer.
Manuel was central to their opening try four minutes later as New Zealand hoovered up scrappy possession on halfway. The tricky centre led a break down the left wing and full-back Winiata took the scoring pass to go over.
Brazier missed the conversion before another harsh call went against Ireland - referee Leah Berard ruled that Lynne Cantwell's pass to the onrushing Briggs was forward. Replays showed otherwise.
However, Ireland responded in the best possible fashion. Clever play from the forwards and scrum half Tania Rosser, winning her 50th Irish cap against her native country, saw them gain ground with pick and goes around the fringes.
They exploited the space to telling effect as they inched closer to the try-line and in the 34th minute, number 8 Highfield's O'Brien burrowed over under the shadow of the posts for a deserved seven-pointer.
That got Ireland off the mark and they kept the Black Ferns at bay from a close-in lineout approaching half-time, meaning the sides went in at the interval with just a point separating them.
Jenny Murphy, who starred in the 'impact sub' role last time out, bounced into action on the resumption. The centre used her physicality to wrestle back possession for Ireland on two occasions.
Brian Evans' pool leaders were clearly improving through and as the minutes ticked by, they were forcing more errors from the Irish. Brazier slotted over a 47th minute penalty after Cantwell had produced a crucial tackle on Winiata.
Winiata and company put better width on the ball as New Zealand threaten to increase their 11-7 buffer, with only stubborn defence from Ireland keeping them out.
Openside Molloy, one of the real heroines of the pack, made two textbook tackles in a row that led to a New Zealand knock-on. Three minutes later, Rosser succeeded in holding up Winiata past the Irish try-line following a threatening break from winger Honey Hireme.
But Ireland finally lifted the siege with a strong Murphy tackle, a Miller poach at a ruck and then a relieving Nora Stapleton clearance.
Their failure to turn pressure into points seemed to rock New Zealand and a wayward chip kick from Renee Wickliffe was pounced upon by Briggs, who stepped past the winger and set the wheels in motion for Ireland's second try.
Briggs carried forward over halfway and passed to the supporting Miller who burst around the covering Emma Jensen. The Portlaoise flyer, a noted finisher at Six Nations level, had the gas to get over in the left corner despite a despairing tackle from Brazier.
It was a rousing effort and Briggs delighted the vocal Irish support with a tremendous conversion from a distance of 44 metres.
Ireland were brought back down to earth within five minutes when Brazier punished the industrious Fitzpatrick for failing to release a tackled player.
Once again though, the girls in green were undeterred. They nipped back ahead on the 70-minute mark thanks to Briggs' reliable right boot , her penalty finishing off great link work by Munster's O'Brien and Rosser at a scrum and a purposeful charge along the right touchline from Ashleigh Baxter.
Tension gripped pitch 1 at French Rugby headquarters as Ireland then had to scramble back to keep the fast-breaking Linda Itunu and scrum half Jensen out of their 22.
O'Brien came up trumps with another terrific carry off the base of a scrum and Briggs' thumping touchfinder gave Ireland the territory they craved.
Although New Zealand did look dangerous from deep late on, Ireland managed to win back possession - thanks to Rosser's harrying at a scrum, a crunching Cantwell tackle and Gillian Bourke's excellent positioning at ruck time - and they duly controlled the ball right up to the final whistle, ending the game in sight of the New Zealand whitewash.
TIME LINE: 6 minutes - Ireland penalty: missed by Niamh Briggs - 0-0; 22 mins - New Zealand penalty: Kelly Brazier - 3-0; 26 mins - New Zealand try: Selica Winiata - 8-0; conversion: missed by Kelly Brazier - 8-0; 34 mins - Ireland try: Heather O'Brien - 8-5; conversion: Niamh Briggs - 8-7; Half-time - New Zealand 8 Ireland 7; 47 mins - New Zealand penalty: Kelly Brazier - 11-7; 60 mins - Ireland try: Alison Miller - 11-12; conversion: Niamh Briggs - 11-14; 65 mins - New Zealand penalty: Kelly Brazier - 14-14; 70 mins - Ireland penalty: Niamh Briggs - 14-17; Full-time - New Zealand 14 Ireland 17
Referee: Leah Berard (USA)
Munster hooker Gillian Bourke (left) celebrates after the game.