After the Breakers posted 7-259, the Fire fought to the end but were never quite in the hunt, bowled out for 228 after 47.2 overs at North Sydney Oval.
Queensland looked gone when top-scorer Delissa Kimmince (44) was smartly stumped by Alyssa Healy before Jemma Barsby (36no) and No.11 Georgia Redmayne (18) did their best to concoct a last-minute miracle.
The pair combined for an enterprising 38-run 10th-wicket stand before Nicola Carey (3-39) disturbed Prestwidge's castle to deliver NSW their 20th WNCL crown in the 23-year existence of the competition.
The result also eased some of the pain of last month's WBBL finals series in which the Brisbane Heat won their maiden title with wins over the Thunder (semifinal) and Sixers (final).
"Our top order really did a good job, excluding myself. They should be really proud," Healy said.
"We've got an amazingly experienced group and some really exciting youngsters.
"I cant wait for the future of NSW, it's looking really bright."
Captain Kirby Short fell cheaply to a wonderful Ellyse Perry outfield catch and the Fire were constantly playing catch-up, with Beth Mooney (35) and Laura Harris (25) both failing to capitalise on promising starts as the rest of the top order failed to ignite.
Soon after Mooney was bowled by Carey, the heavens opened, forcing players off the field momentarily.
Harris departed to a fine diving catch from Rachael Haynes and despite the lower-order efforts of Kimmince, Barsby and Prestwidge, the Breakers' total always appeared out of reach.
Earlier, NSW started disastrously when captain Healy was plumb lbw, shouldering arms for a duck off the third ball of the morning.
Ellyse Perry then fell leg-before for 31 in her final game for NSW before moving to Victoria next season to join her international rugby-playing husband Matt Toomua in Melbourne.
Haynes (79) and player-of-the-match Carey (50) put the Breakers in the box seat with a 103-run third-wicket union which ultimately proved the difference.
"All around, they were just a little bit too good for us," Short conceded.
"(I'm) proud of the scrap to get it to the last couple of overs but probably just a few too many runs scored (conceded) for us to chase."